Hey I like Visual Thesaurus (can't quite see me spending $30 on it though)
Another good similar app is WordWeb. There is a free version (http://wordweb.info/free/
) and also the Pro version (which costs $19).
It is nice because it links in to all applications for spell and replace (just highlight a word and hit Ctrl/Alt+W and it pops up), plus there is a great anagram solving section etc.
The other program I really like from the same author (Anthony Lewis) is Crossword Compiler (see http://www.crossword-compiler.com/
). This not only helps you to generate Crosswords in all sorts of styles and layouts but also produces interactive Webpages to solve them ...
Anthony is excellent too at constantly updating the programs with lots of ideas (Crossword Compiler has just been extended to generate Sudoku puzzles), and responds to emails very quickly.