Evernote for iPhone
At the moment I actually carry two phones around â€“ my HTC 7 Trophy and my old HTC HD2 running WM 6.5. The only reason I am still carrying the beast around is due to the lack of a good note-keeping app on Windows Phone 7 (curse you Phatnotes!)
It seems that this problem may not last forever however, with the Evernote podcast announcing that a client for Windows phone 7 will be making its way to Marketplace soon (around the 40 min mark). The company has apparently hired a dedicated developer, and is in the final stretch of development.
Hopefully the app will serve my needs well, and another Windows Mobile device can be retired.