Got catgirl mod, and a few other random ones around.
Suggest others? No Graphics enhancements, picture below will show why. Currently running on a low Res with graphics waaaay down. Though I did turn it up since the pic was taken.
What I'm currently running is Oblivion XP (Xp-based leveling system), OOO (Huge overhaul of Oblivion, changing the enemy leveling system and many other aspects in the game, making it more challenging but rewarding, only use if you want a challenge), Kvatch Rebuild (Name says all), Midas Spells (Adds tons of unique spells, very fun) and some more that add Questlines, towns, and so on. You could try to browse the Oblivion Nexus for categories.
The only ones I know of are the official add-ons, like Knights of the Nine and Shivering Isles. They're fun, but probably not free. I'm limited in my 'Blivion modding due to X-Bawks.
But my sister got it on PC a while back, and she's having a lot of fun with the Clock Mod. It puts functioning clocks in specific places, and adds a large clock-tower to the middle of each city. It doesn't sound all that interesting, but she seems to love it.
I currently have only All Natural and Immersive interiors huuuuuge difference in the depth of the game coming from something so simple as being able to see the town through the windows of your house
Well, I could list a bunch of cool stuff like the Natural Weather/Water/Fauna mods but they drop FPS on you like a...
I do know there are quite a few streamline mods such as the lowpoly grass mod that keeps the quality yet makes it easier on your computer. Search the Nexus for low poly or graphics mods which do that. It'll help!