Windows only: Freeware application ClipCase formats the text in your clipboard in a number of very useful ways—from line break removal to different capitalization schemes—designed to help you clean up text before you paste it elsewhere.
The most useful features of ClipCase are probably the "Remove returns" functionality and maybe even the "Remove >" (handy for copying email quotes). The text transformation stuff is fun, but other than the "Cap sentences" option, which makes sure you've capitalized the beginning of every sentence, I'm not really sure why you'd make much use of it. Either way, ClipCase should come in handy for anyone who does a lot of copying and pasting of text. ClipCase is freeware, Windows only. For more clipboard formatting, check out Text Scrubber or PureText.