AIM 6.8 Beta includes real-time IM: Freudian slips not just a vocal problem
The new feature is incompatible with iChat, Pidgin, and other third party IM clients, but if this catches on, it's likely they'll add support to for real-time IM soon. For now, if you'd like to use this feature, you'll need to use the official AIM client.
Real-time IM requires one of the users to activate a direct connection. The other party may choose to decline, so at least it's optional. Though it may seem "regular" and "bland", the ability to edit instant messages is a blessing. Maybe we're just a bit geekier and a little more old-fashioned than the average person, but we've been caught in way too many awkward, verbal situations because of something as minor as a forgotten name (it's hard to remember everyone from high school, dammit).