More Mac 101, TUAW tips for new and returning Mac users. If you're typing in a text field (in Safari, TextEdit, or most any Mac OS X app), you can press F5 while your cursor rests in a particular word to see a list of words that begin with the letters after the last space.
Holding down Option and Pressing Escape works, too.
So, for example, if you type create, you get a list of words including create, created, and creates.
If there are a lot of words in the list, it only shows the first 100 results, sorted alphabetically. The results come from Mac OS X's built-in dictionary.
This trick is useful for when you have a word on the tip of your tongue, need help with possessive apostrophes, or are stuck on a crossword clue.