+1 for iStat.
I used it the other day to find out that my little sister's PBG4's battery had close to 800 cycles on it. I have it on my iPod Touch because it helps clear ram and shows me my MAC address, it also tells me the stat's of my MBP with "iStat Server" wirelessly via Bonjour. It's awesome, I was going to donate until I found the iPod app, bought it instead.