Yes, you absolutely need For Sale. It's different enough to provide a new experience, plus similar enough that you know your crowd will enjoy it. If nothing else, ou should use it to avoid getting "burned" with High Society --you know the feeling, when you have played a game so much it actually starts to bore you.
If your group enjoys those games, you'll probably have fun with Coloretto. For slightly more social mechanic, try Saboteur. And if you have weird senses of humor, try Give Me The Brain or Lord of the Fries (I prefere the first). The last two are particularly cheap.