I completely disagree with the two posters above. There's a huge array of KotOR mods out there, and while some are purely cosmetic, there are plenty which aren't. Personally, I think the KotOR I list found there is incredibly limited. Some of the more substantial mods which (IMO) enhance the game hugely:
KotOR I Restoration 0.9 by ZM90, Fair Strides, et al. (and the bugfix ;
Brotherhood of Shadow: Solomon's Revenge by Silveredge9 and v1.1 patch
ORD Mandell by RedHawke (NB: this one doesn't use the patcher, so install it before anything else if you're going to use it. The same applies to RedHawke's other modules, e.g., the Tatooine jawa shop mod.)
Tomb of Jesset Dal'Kest by Darkkender
Korriban Crystal Cave by Agent Xim
Recruitable Kay by Inyri
Sith Stalker 0.9 by jonathan7, VarsityPuppet, Marius Fett, Qui-Gon Glenn, Dak Drexl and redrob41;
Content Pack 1 v1.1 by TamerBill and UnknownJedi
All-in-One Force Power Mod by Darth333, Darth Khasei, etc. (N.B.: Install before everything else if you're going to use it, because it will cause a huge number of incompatibilities otherwise.)
Quanon's Temple mod (N.B.: Not compatible with the Korriban Crystal Cave)
Endar Spire Dialogue Enhancement by CarboCation
Kill Yuka Laka by Darth333
Kill Star Forge Jedi by Sareth154
Tatooine Spice Dealer by Inyri Forge
Force Pack 2.0 by Star Admiral
Personally, I find the following 'cosmetic' mods also massively enhance the game:
Weapon Model Overhaul by Toasty Fresh
Praetorian Armour by Quanon
Weapons of the Old Republic by T7Nowhere
Lightsaber 7 Pack by T7Nowhere
Revan's Mask Plus by T7Nowhere
HV-88 by svosh
90SK's K1 Robes (plus patch )
MedHypo by Rtas Vadum
Darth Malak - Dark Lord of the Sith by Drewton
Vibrosword Replacement Pack by DeadMan
Saber and Melee Weapon Sound Mod by DeadMan
Ajunta Pall Unique Appearance by Silveredge9
Revan's Flowing Cape and Belt by SithSpecter
Male Head Pack by Inyri Forge
Bryar Pistol and Bryar Rifle by Inyri Forge
Ryyk Blade by Inyri Forge
KotOR Repulsor Shields by Inyri Forge
And finally, I don't think a good number of my mods would fall under "cosmetic" changes:
Korriban Academy Workbench (N.B.: Install this first, if using it with the Lightsaber Forms mod)
Granted, I've also released some which are cosmetic, e.g.:
but most of my new item mods have, I like to think, something a bit more to them:
Extreme Conditions Combat Robes
If OP really wants to check out what KotOR mods there are, though, I suggest he visit the DeadlyStream KotOR downloads page, as well as KotORFiles' K1 mod index. For completeness' sake, you could also check out Lucasforums' KotOR mods release section, and the KotORNexus, but anything in the first two is going to be in the last two as well, so finding stuff additional to that is going to take a lot of trawling.