If you're a Twitter Addict (ahem), and your followers have come to expect your exiting tweet-on-the-hour updates, don't leave them hanging if you're out of cell range, on a plane, or hey, even sleeping. Check out Tweetlater to schedule your tweets in advance, and keep 'em coming 24 hours a day.
But Tweetlater doesn't just help you schedule tweets, it can help you track keywords in the public Twitter stream, and send automated thank-you notes to new followers.
The cost to use Tweetlater? Nada. You can thank me later.