From KEDMI Scientific Computing:
TinySpell Portable allows you to easily and quickly check and correct the spelling of words in any Windows application. It can watch your typing on-the-fly and alert you whenever it detects a misspelled word. It can also check the spelling of the text you copy to the clipboard. TinySpell installs itself in the system tray for easy access. It comes with an American-English dictionary containing more than 110,000 words.