Twuffer

Twuffer – schedule future Tweets. Why? Recommended uses include:

• Tweet hourly/daily/monthly announcements
• appointment/milestone reminders
• run a time-based scavenger hunt
• notify subscribers about upcoming podcast or video episodes
• appear to never sleep

Easy Tweets

Easy Tweets – manage your multiple Twitter accounts, schedule Tweets for future posting and add RSS feeds for auto posting.

twitabit

twitabit – another service that allows you to post Tweets even when Twitter is down.

Twiddict

Twiddict – when Twitter is down post your Tweets to Twiddict and they by be stored for posting when Twitter is all better again.

TweetLater

TweetLater – schedule Tweets to post at a later date.

TwitResponse

TwitResponse – Twitter + Autoresponder. Will post Tweets at a time specified by you.