Twitbit [$4.99 - iTunes link] is a Twitter client for the iPhone and iPod touch that provides built-in push notification for @mentions and direct messages (DMs).
For those of you still reading -- those didn't immediately jump over to grab it -- what this means is you get all the functionality you've come to expect -- reading, posting, multiple accounts, start and stop following, searching, trends, user profiles, reply chains, etc. etc. and you get any @mentions and DMs pushed straight to you without the need for an extra enabler app (which most other Twitter clients currently require).
The folks at High Order Bit were gracious enough to give us a sneak peak to try out, and I've been using it pretty much non-stop since. And... I've found all the functionality I need and then some. The push works wonderfully as well. So far, so fast.
One thing I particularly liked (but others may not) is that, when you get multiple @mentions or DMs, rather than having the latest obliterate the previous text alert (fix that by implementing a genius stacking system, will you Apple?), Twitbit collates them up. You don't get to see the contents of the latest message, but you do get to see "X new @mentions and X new DMs" (see screenshot below). At least you have some idea of volume.
Of course, iPhone notifications being interruptive as they are, there's still a chance something will pop up while you're watching a movie or playing a game...
Given that limitation, more granularity as to who and what Twitbit pushes would be grand -- and it's likely forthcoming in an update -- but wow are these young upstart devs and apps giving the entrenched Twitter clients a race for their functionality.
If you want an amply functioning Twitter client with built-in push notifications, take a serious look at Twitbit and let us know what you think.
Tons of screenshots after the break!