Here are a couple of my Must-Haves.
Act 1: Fantastic video player, especially with the "Resume" widget for it.
RedLaser: Barcode scanner that gives all kinds of information on what you scan, from where to buy and how much, to calories on food products.
Netflix: Not the queue manager, the actual one from Netflix to watch movies with.
X-Plore: Basically a file manager program.
Subsonic: Stream Music and Movies from your home computer to your phone. Fantastic program, definately a must have.
GTunes: Free music downloader.
SoundHound: In my opinion much better than Shazam.
Old Time Radio: Free radio shows from the 40's and 50's. What can i say, I love those old things. Fibber Mghee and Molly, Great Gildersleave, Flash Gordon, Dimension X.
AirPush Detector: Tells you what programs are pushing ads to your phone so you can kill them off.
Catch: Yeah, it's already mentioned here, but wanted to give it a plug anyhow.
OnTheFly Backup: Backs up your apps to the SD card so you can restore them if something drastic happens to your phone.
PdaNet: Teather program.
And finally, Vlingo: Kinda like Siri, sort of. And it's quite good at reading your incoming txt messages without having to actually unlock the phone.
I hope someone gets some nice ideas from my list. I always look here for suggestions for myself as well. You folks always have some great suggestions.