When I jailbreak my iphone, here are the first 5 apps I install straight off.  

1) Unix tools (esp. SSH and Terminal) .  If you have to ask, you do not need it

2) Videorecoder – The only bummer is this app does not work on 2.1 right now. I use QIK for now. Its curious to me that apple has not put video in the phone. I still have the feeling they are going to partner with someone to release it thought the store for 9.99.   Even 1/2 a million downloads is $5m.  You KNOW they are not going to leave that kind of money on the table. 

3) Categories – This is a new application that allows you to put icons into folders. The moment I saw this, I knew it would be a most have. My iphone is much cleaner now. 

4) BossPrefs – This app also has minor issues in 2.1.  When you turn 3G on or off it will sometimes turn wifi off.  I’m sure they will fix this soon.

5) Customize – Although you can change almost anything about the graphics and sounds through this app, for me, I use it for one thing.  Change the alarm to something that will actually wake me up. 🙂