Been using a really cool (and free) service called Jott. You register your email and cell phone number with them (they promise not to share/spam), then you can call their 800 number from your cell and dictate a short message to yourself. They transcribe it to text and email you your message.
When I'm in the car driving I always think of things I need to do and ideas for work but I have not until now found a good capture method. I hate trying to leave voice notes on my crappy cell phone (it's near the end of its 2-year life and is slow to respond to side button commands, plus I just don't have a good routine of processing the voice notes.) So with Jott I just hit 5 on speed dial and speak whatever I need to remember the item and there's a reminder in my email (where I do most inbox-processing anyway.) So this fits nicely into my GTD system and helps me get ideas and reminders out of my head and onto a list.
Hope Jott finds some way to monetize this. I wouldn't mind seeing a couple of ads in the reminder emails.