I've got a little time now so i'll do a run down of whats good and what to see. I can tailor it a bit better if you let me know roughly where your staying, if you have use of a car or are relying on public transport. Perth is a big place and the breweries are spread out.
First thing I want to clear up is the problem with Little Creatures. If you ask anywhere people will tell you it's the best beer in perth and the best venue. While I will admit I don't mind there latest pale ale and the IPA I try not to support them on principle as they are part of Lion Nathan which is sort of the southern hemisphere version of AB INBEV or Miller Coors the big bad guys. Also they are Japanese owned and i'd rather my beer money stays in the country. That's my personal feelings about it but by all means make sure you give there beers a go and maybe even check out the venue in Freo it is nice but quite expensive.
There are 3 main areas for beer in perth, The Swan Valley (30mins), Fremantle (30 mins) and Margaret River (2.5 hrs). The times in the brackets are approx times from the city driving. So depending on the time you want to allocate to beer the first two are probably going to be your best bet. If your already heading to Margaret River then that's a plus it's a real touristy area and has some great breweries.
Swan Valley is probably has the bulk of the breweries and there is a lot of other cool stuff to do out that way a few distilleries, chocolate factory and wineries.
The must see brewery of WA is Feral in the swan valley, these guys make a beer called Hop Hog which has won heaps of awards and they bottle it so it has a lot of coverage. Decent enough beer but they keep all the good stuff at the brewery on tap. They are the first brewer in WA to also start dabbling in sour beers. I think at the moment they have 3 or 4 on regular. A Berliner Weiss a geuze style and I think the same beer blended with something else so it's less sour. They also have a lot of great barrel aged beers my personal fave if I had to pick one is the BFH. They use new french so it's got an interesting character. The barley wine and russian imperial stouts are also good. If your heading here on the weekend make sure you book a table. Service and food seems to have dropped a little in recent years but it's reasonable enough. Take away bottles are available at the bar. https://www.feralbrewing.com.au/
Mash are another really good brewery they won the AIBA beer of the year award last year for there Copy Cat IPA so definitely give that a go as it's technically the best beer in Australia. The venue can be a bit odd you need to book on weekends but it's also out the front of a super golf place so you get a lot of walk ins bachelor parties and hens nights etc. can be rowdy, less so on week days. Mash sell bottles from the brewery I believe. http://www.mashbrewing.com/
There is a relatively new brewery call Homestead out that way that I haven't been out to yet. It's always getting recommended to me by friend and they have a good name the brewer is also from a succesful Victorian brewery I believe. I've only had their black IPA on tap at the pub it was very good and I find BIPA a bit of a meh style. Apparently they have a really nice venue too it's shared with a winery. https://www.mandoonestate.com.au/homestead/
Swan Valley is home to two German brewerys, Elmars and the Duckstein. Both are good, the beers are traditional German style beers. So while not being overly adventurous they are still tastey beers to be had from both. If I had to pick on it would be Elmars, their beer is really nice and there food is amazing if you like German food. Elmars also have a great small good deli section. Duckstein do some bottles but i'm not sure if it's the sort of thing you would want to take home.
Last but not least is Iron Bark Brewery. This place is a whole different kettle of fish. The venue is a little bit different, with its wonky paving and miss matched furniture. Don't let that put you off it's got some great beers. My friend tells me that the beers are all decoction mashed and that's what gives them their great maltiness.
List all breweries in WA: http://www.waba.org.au/breweries.html
Swan Valley brewery page and tourist info: http://www.swanvalley.com.au/Attractions_and_Experiences/Breweries