Root Explorer
Auto-killer Memory Optimizer (A stock Rom must have)
No-frills CPU
Cache Mate
Juice Defender Ultimate (Works best with stock based Roms)
Titanium Backup (many features besides backing up Apps)
Chainfire3D (Makes unplayable high-end games playable on the Triumph)
SD-booster (512 or 1024mb SD-card cache speeds things up a bit)
Incredicontrol (CM7 only, to my knowledge)
More then five but my list changes depending on Rom, CM7 for example is the only Rom that Incredicontrol can be used with to my knowledge and also already has the SD-booster optimization included. Also, not a fan of Ad-free as many developers can only offer free Apps based on ad Revenue, would think about this before using.