TweetDeck is great for serious Twitterers: A desktop application that lets you split your main feed into topic or group specific columns. Also has filter options and auto updates. Related posts: Turn Web Apps Into Desktop Mac Applications Join Twibes Twitter Groups Who’s The Ultimate Twitterholic?
Tweetree: View your tweets’ replies easily, including external content like TwitPic and Flickr photos, YouTube videos and more without having to click through links. Related posts: Make Twitter Better External Link WordPress Plugin YouTube to MP3 Converter
Find mutual friends, use bulk un-follow option and create lists for only friends or only followers, all friends or all followers, and mutual friends with Dossy’s Twitter app. Related posts: Visual Twitter Network Browser Verify Your New Twitter Followers Conversations On Twitter
Leapfish: The slogan in their search box says it all: you can choose from Google, Yahoo and MSN and get instant web, blog, images, news and video results on one page. Nice! Related posts: Instant YouTube Search Monthly Keyword Search Volume Compare Yahoo and Google Search Results