While there are tons of things I love about my jailbroken iPhone 3G (OpenSSH, VNC, Google Voice), I have a few favorite apps. As I’m cheap, all of these are free, save for my #1, which was well worth the $0.99:

5. Five Icon Dock lets you add an extra icon. Yeah, it seems trivial at first glance, but you can put all four Stacks on your dock, plus still have single-touch access to a fifth icon. Mine has my Phone first, followed by a Stack called “Apple” (with SMS, iPod, Mail, etc), a Stack called “Web”, a Stack for “Games”, and a Stack for “Utilities”.
4. Stack v3 gives you sort of an instant categorization view. I put mine on my Five Icon Dock, which gives me access to about 90% of what I do every day within two touches of any screen.
3. The 3G has a camera, but only the 3GS an newer can shoot video… until now. Cycorder gives you 15 FPS video on your 3G.
2. Apple might have added multitasking to iPhone OS 4, but they won’t enable it on the iPhone 3G. Get ProSwitcher and listen to Pandora or Slacker while running other Apps.
1. If you have iPod/iPhone accessories which aren’t “Apple Certified”, you’re probably tired of the Airplane Mode warning. I found it annoying when I would occasionally use the USA Spec iPod Integration in my MDX, but with the iPod/iPhone alarm clock I got for fathers day, I suddenly found myself anooyed every night. Fro $0.99, Popup Blocker is my sanity savior, allowing me to block dozens of different types of nusiance alerts.