Evernote. But they are on a roll. First they release version 2.0 of their Android client, and they hit 5 million users.
Now today, I awoke to find a new version of Evernote for my iPod and my iPad in the Apple App Store.
And the next issue of their podcast is out.
The best tool keeps getting better.
I plan another major post about Evernote once Due Dates are added, akin to recently updated "Your First Day with Evernote".