Download: Stuffit Archive
"This service calculates the result of a selected formula within all Cocoa-applications (e.g. Textedit, Mail, Stickies, Notes, ProjectBuilder, Fire, OmniWeb or TeXShop) and appends the result to the formula or replaces the formula with the result. In addition there's the possibility to display the result in a panel without modifying the text. So there's no more need to start Calculator or stuff like that if you only want to calculate some values immediately within text-windows or dialog-fields."