I use Jott to send notes to myself. Have the Jott for iPhone app, but prefer to email a note to myself by phoning a note to Jott.
Re: GTD apps ... I prefer OmniFocus. Briefly tried Remember the Milk. It's okay if you follow the GTD set-up tutorial. However, with RTM you have to manually designate NA's whereas OmniFocus automates the process.
Experimented with Toodledo (web) and ToDo (iPhone) also. But to me, the combo seems inefficient as compared to OmniFocus. I'm no shill for Omni Group, just a devotee.
OmniFocus for Mac desktop + iPhone is an expensive pair of apps, but it has streamlined my workflow appreciably.