Every now and then when I try to access my Tab-menu, the game freezes and I need to end the process via the Task Manager. It could be a mod, but I don't think so. The problem isn't there being too much stuff in my inventory, because I've experienced slowdown from that in the past and this isn't it. I also know that the UI mod I'm running isn't it, because I added it after this problem started happening.

I am running the following mods:

Atmospheric Loading Screens
Bank of Cyrodiil
Call Steed/Saddlebags
City Gates
Conduit Magic
Curse of Hircine
DarNified UI
Dwenmer Skyship
Elsweyr Anequina
Extended Imperial City
FastExit
Hoarfrost Castle
Keychain
Kvatch Rebuilt
Map Marker Overhaul
Merchant Inventory Realism
Midas Magic Spells of Aurum
Midas Oscruo Gems
Oscuro's Oblivion Overhaul
Portable Campsite
Stirk
Universal Armor Stand
All Unofficial Patches
Windom Earle's Oblivion Crash Prevention System

And, naturally, Oblivion Script Extender. Also, I'm using the GotY edition, plus SI.
I got most of these mods from tesnexus.com.

Would someone help, puh-LEEEEEEEASE?

I just did a reinstall, kept all the mods and savegames, and the problem came back after 10/20 minutes of problem-free gameplay.

Does the problem occur when you run the game with no mods?

You should post a proper load order otherwise nobody can see exactly what esps you have active (or not) and what order they are in which can also cause problems. If you don't know how to do that check http://sites.google.com/site/oblivionpoinfo/troubleshooting/postlo.

I found what the problem was: the Keychain mod I had was multiplying random keys such that I had 120 million of them (at one point). It may have been trying to list them all individually whenever the game crashed. The UI mod makes the Keychain one obsolete though, so no worries.