Android: A good number of Android users dig the slide-to-type Swype keyboard, but that's now a closed beta. SlideIT is an alternative swipe-style keyboard, and if you find one-handed typing a pain, it might be right up your alley.
SlideIT works just like Swype in its basic functionality. Instead of tapping each letter of a word, you slide your finger along the letters in succession. In a surprising number of cases, SlideIT figures out what you were going for, based on your turns, hesitations and general letter order. If it doesn't pin it down exactly, it offers you a familiar assortment of guesses from the dictionary, and you can add your own words to the dictionary as well.
My main gripes, and I'm not alone in them, are the generally lo-res look of the keyboard on higher-resolution phones like the Droid or Nexus, and some occasional problems with double letters — you're supposed to do a little loop to hit the letter twice, but it's an inelegant solution at the moment. Still, on the whole, I was able to send out text messages this morning much faster than pecking with a thumb while holding the phone portrait style.
SlideIT is offered as a free Lite download and a full-fledged version, with lots of language packs available.