I use Handcent and love it on my Atrix. You can set up the Pop Screen to wake your phone, for a certain period of time, then go back to sleep. (The pop up box will still be there, even when the screen is off.) You can do a quick reply, while the screen is still locked. Just recently, they added a schedule task text option. I haven't tried it yet, but looks like it works well, for sending text out on a certain day, time and can repeat.
I would have to say I really love the customization of Handcent the most. I can change the skin, conversation list and bubble settings to my liking. I just figured out, that I can have a different picture, as the background, in the contact list and conversation view.