Hey guys I have been jailbreaking since iOS 4. Here is a list of awesome tweaks for your device. All the tweaks work flawlessly on my iPhone 6, iOS 9.0.2. There is no excess battery drain. I have never faced any crashes on my devices ( I had an iPhone 4 and 5 before this) . Some of the above tweaks aren't free but they are worth the price. There are no redundant tweaks.
Activator - You can assign custom events for every action. Eg. Change music with volume buttons, turn on location services as soon as you launch google maps, etc.
AppColorClose - Tints the small 'x' button while deleting an app with the colour of app icon. Really cool.
Apple File Conduit '2' - Access iPhone system files over USB for use with apps like ifunbox. Only for experienced users.
AppPlus for snapchat/ Phantom - Removes all snapchat restrictions. You can view snaps unlimited number of times, save them without the sender knowing, etc. AppPlus has no ads.
ayeris - Best theme in cydia in my opinion .
Bariol iOS 9 - Best font in cydia in my opinion.
betterFiveIconDock - Put five icons in dock.
BreadCrumbArrow - While switching apps it only keeps the arrow so that you can still see the carrier info.
Bytafont 3 - Platform to apply the font mentioned above.
CallConnect - Phone vibrates when call is connected so you don't have to keep staring at the screen waiting for the caller to pick up.
CellularUsageOrder - Reorders the apps in the usage menu by cellular usage . CheeseCake - Android L's screen lock animation. Subtle and cool.
Colorbanners - Tints notifications on lockscreen with the colour of the app. Like green for whatsapp and blue for Facebook. Looks awesome.
Coreba - Install with RevealMenu mentioned below. For 3D Touch.
Crash Reporter - To identify the reasons for your phone crashing. Works most of time.
CustomCover - Tints the entire music app and the lockscreen with the now playing music album artwork. Looks amazing.
DetailedBatteryUsage - Useful for determining the true cause for battery drain. Unlocks hidden system battery draining processes in the battery menu.
EnableLivePhotos - The new Live Photos feature on any iOS device.
Filza File Manager/iFile - Proper file manager for iOS. Based on recent developments, Filza seems to have more functionality.
FlipControlCenter - Customise the CC switches. Like you can add low power mode and location services switches to your CC. Again very customisable.
HideMeX (iOS 9) - Customise every part of your iOS device. Too many features to list. Check it out.
iCleaner - Removes junk files from your iOS device. The best cleaner available.
IllLooklater - Prevent your phone from waking up the screen for every notification. I've turned it on for some news apps, as I can look at all the notifications together when I'm free. Saves battery.
InstaBetter - Best Instagram tweak. Save images and whatnot.
KuaiDial - Adds a T9 dictionary to phone app. Like when you type half a number it shows the full number if it is in your contact list like android.
Livewallenabler - Live wallpapers on iPhone 6. Also includes a link to download the iPhone 6S wallpapers. Works perfectly.
LockHTML 4 - Theme your lockscreen. Incredible customisation for the lockscreen. Check out r/iOSthemes for examples.
*Minimal HUD - Replaces the annoying volume display with a small bar at the side. No more missing a couple of seconds of video while adjusting volume.
MusicMod - Makes the music player like the old one. I have enabled all features. So now I have only My Music and Playlist tabs in my music app. Also includes swipe gestures to change music. Safe to say I don't like Apple Music.
No Music Downloaded Indicator - Remove 'downloaded' word in music app.
NoAppStoreRedirect - Apps won't redirect to AppStore but will open a prompt. Required when you are a gamer and click on an ad accidentally.
NoMotion - Removes the unnecessary parallax effect in iOS. Saves battery
NoTracking+ - Stops apps like Facebook from tracking you. Saves battery.
OneTapClear - In the Notification Center, just tap on 'x' to clear the notification. God knows why Apple made it so we have to tap twice.
Placeholder - Adds a setting app icon to cydia tweaks that don't have an app icon. Useful for people with OCD.
Power Tap - When you press and hold power button, you can tap on the slide to power off logo and get options like slide to respring, reboot, etc. Very minimalistic and very cool.
Power Banners - no more getting interrupted by '20% battery remaining'. It changes to a banner.
PrefSafety - Disables reset all settings in settings app. Coz you should protect that jailbreak!
Priority Hub - Organises notifications app wise like BBM on the lockscreen. Seriously awesome.
Repair Settings Layout - In iOS 9, the settings app doesn't open at the correct height. The search bar isn't visible. This tweak fixes that. For people with OCD.
RevealMenu - 3D Touch on all iOS devices. Works like a charm. Even has peek and pop but I don't use that anyways. Install with Coreba mentioned above. Just press and hold on an app to see.
RoundedMusic - Makes songs inside the music app have round icons. Small tweak but I like it.
Rubik - Turns off 3G when locked. I only use it as it comes with a 3G flipswitch for CC. I don't use the auto off option. Can't comment on it.
Shortcuts - Add more menus when you 3D Touch certain icons. Like settings app. Works flawlessly with RevealMenu.
ShowALLChanges - In cydia changes tab, it shows updates for all apps in cydia in the recent section and not only apps which you have installed. Really cool now you can keep track of all the apps!
Shy Page Dots - Only show page dots while scrolling. Nice little tweak.
SimpleCenters - customise the NC and CC. Now I know HideMe X has most of the functionality offered by this tweak but I use it for 1 thing - if I have pending notifications, it opens NC to the notifications tab . Otherwise it opens to the today tab. Really neat.
SmoothCursor - Makes your cursor smooth like in Office 2013. Open the notes app and check it out!
Stalky - Adds a small button in whatsapp where you can see all status and profile pics that your friends update. Saves a lot of time in stalking those 400 friends. Keep background fetch off however. It drains battery.
StopClock - Stops the clock's second hand from moving on the springboard. Saves battery.
Swipe Home - Swipe up the home card in switcher view to kill all apps. Useful when you have a lot of apps open.
SwipeSelection - Swipe your finger left or right to move the cursor. Really speeds up typing.
SwitcherTweak - Open the switcher view from the right side and not left. Looks better this way.
TapTapFlip - Tap on the screen twice while the camera is open to flip it. Like snapchat.
Tinybar - The notifications size by default are too big. This makes them smaller and even scrollable.
TransparentCameraBar - The iPhone 6 has such a big screen but half of it remains black in camera view. This tweak makes those black bars go away! Really cool.
VideoPlayerRotatable - Disables Rotation lock when video is played and enables it again when it stops playing. Works like a charm. Only one small problem is that it recognises live wallpapers as a video so it unlocks the rotation lock when you use a live wallpaper on lockscreen. But it's a small issue nonetheless.
VirtualHome 8 n 9 - So awesome! Never press the home button again. Just tap on it to close the app. Double tap to open the app switcher. Tap and keep finger on the button to put the phone to sleep. 1st tweak I install. Keep in mind to keep quick unlock and vibrations off. That drains a lot of battery.
Watusi - Best tweak for whatsapp. Has really cool privacy and theming features. You can also send unlimited photos at once.
Winterboard - Theming platform to apply the theme ayeris mentioned above.
Here are the tweaks that I'm waiting for to be updated for iOS 9 -
AirBlue Sharing - Send and receive any file over Bluetooth with any device, including android and windows.
CircleIcons - Makes the settings icons circular. Because I want everything to be circular.
GroupSend - Send messages to a lot of people without having to again and again press on that small plus button and select a contact.
LockGlyph - Apple Pay animation when you unlock device. Doesn't work with LiveWallEnabler.
Seng - Better than auxo. Merges app switcher and CC. Really awesome.
SmartClose - Saves battery. Don't know what the hell it does till date.
Springtomize - Complete iOS customisation like HideMe X.
Now I might have made some mistakes in the info above or might have missed some must have tweaks. Kindly comment below and I'll check them out and add them above. This is an awesome community and I hope the above list helps out some people.