Although there are a bunch out there, Marshall Bock’s iPhone PSD template is the best I’ve come across. Not only is it constructed from vector artwork but it contains every combination of iPhone 4, 4S, black, white, portrait and landscape you could ever want.
Brilliant.
WDL has a list of 10 ‘excellent’ tools for producing wireframes. There are some good ones here — I have a little experience with Axure & Mockingbird looks very interesting.
Personally speaking I’m not a fan of stylised wireframes (like the ones produced by Balsamiq or Cacoo) — I feel they detract from the purpose of the wireframe itself and add an unnecessary layer of style. I’ve reviewed many ‘styled’ wireframes in the past and I could never get over the feeling that they were trying too hard.