Check it: --> Tweet Later
Thanks to utterlygeek for the cool site. Tweet Later basically lets you automate your Twitter account. They have a free version which works just fine. Or if you're a super tweeter, you can pay $30 a month and get all kinds of goodies.
Here are some features of the free one:
Schedule tweets — Plan, set & forget!
Track keywords on Twitter — Empower yourself!
Save and reuse drafts — Save hours of typing!
Send welcome DMs to new followers — Automate!
Bit.ly URL shortening — Track those clicks!
Follow those who follow you — Automate!
Unfollow those who unfollow you — Automate!
Unlimited Twitter accounts — No charge!
Now tweet away in the wind.