I just kinda skimmed through the responses here but I wanted to add my 2 cents on lyric and song writing.

Definitely invest a couple of hundred bucks and get yourself a program called MasterWriter.

I've been using it for awhile now and it's invaluable for things like rhymes, thesaurus info, Dictionary, Phrases, Rhymed Phrases, Aliterations, Pop-Culture references etc..
Not to mention a convenient layout to organize your songwriting, sketches, audio and lyrics.

I'm not associated with them in any way but I've been using the program for awhile now and it's invaluable in organizing your ideas and coming up with interesting subjects and tangents to go off on.