Camera+: http://campl.us/ is one of the best camera apps I have on the iPhone.

For Panorama and 360 degree shots try Autostitch and 360. The results are incredible, virtually seamless stitching right on the phone.

Finally for HDR type photos check out Pro HDR. Whenever I want to use HDR photos I tend to gravitate more in using this app over editing on my desktop or using a regular camera, just for the ease of use and great results. The latest version now has filters too.

I love my iPhone.