I use word because i save all my listings and port the verbiage to my various stores.
I select the word icon above the description and paste it into that box. Then I ctrl a (or select the words in the description box) and modify the font and sometimes the size.
It is usually only two steps: pasting into the little word icon box and adjusting the font.
To Vickie's point, notepad is excellent because it tends to strip the html.