I was playing around jotlet's iPhone style icon psd kit last night and came up with two replacement icons.
The first is for MobileChat and the second is for NES. To install these icons, use your preferred method of moving files to your hacked iPhone (scp for example) and place each icon in their application directories (ie: /Applications/Chat.app/ and /Applications/NES.app/) but make sure you change their names to Update: Well that was fast. MobileChat just updated to 1.2 and has a really slick new icon. No need for my own anymore. By the way, putting the .mac account logo in the account manager is so mean when it doens't work yet! Great job anyway though.icon.png, replacing the existing icon.png. The next time you update these apps, the icon will go away, so you'll have to redo this.
I tried a lot of colors behind Adiumy's head but none of them looked right to me so I took all of the colored layers off and used the base transparency layer in the psd icon kit. I think it came out pretty nicely.
The head of Adiumy was manipulated from the default icon that ships with Adium and it's not mine. Also, the head of Mario was photoshopped from this image, which isn't mine either.