I was thinking that I would never jailbreak my iPhone 3G, but the QuickPwn 2.1 came out, and I was kinda bored, so...
The main programs I like are Winterboard and Intelliscreen. With Winterboard, I love having my wallpaper in the background behind the apps. Without that, you hardly see your wallpaper.
With Intelliscreen, you do have to pay either $4.99 or $19.99 if you like it past the 10 day trial, but it's an awesome app. Shows you your upcoming calendar events, e-mails, weather, and news stories without unlocking your phone. Not necessary, but really neat anyway.
I'd like Cycorder more if I could figure out how to transfer the vids to my computer easily. Without that ability, it's kinda useless to me.
One other program I like is Folders. It allows you to put apps into folders to organize your home screens a bit. I have the ones I use most out in the open, and all the apps that I only use occasionally neatly stowed away in folders. I can find the apps without flipping through 8 pages of junk.
Overall, I'm glad I decided to give it a try.