Open Call for Favorite iPhone Apps

I'm late to the iPhone party but I just got my invite last night and have been having a ball playing around with it ever since.

And now I'm starting to move towards making my iPhone all it can be by adding applications, tweaks, GUI personalizations and whatever else I can to make my iPhone cooler than it already is.

If you are using or have heard of any awesome iPhone apps that I should look at then please leave a comment for me. I'd love to get a hack to change the ringer volume adjusting rocker on the side of the phone to do alot more, like scroll and maybe app switching. And I'd love a back button as on my Clie.

I've already updated my iTunes Cover Flow and collected something like 1400 album covers to get my art up to speed. Because flipping through blank album covers is lame and not cool at all.

I'm also in the market for a decent protective case or other carrying mechanism to give it some measure of protection while still being as usable as possible. Any input is welcome.