springs + shocks + bushings
will net you a lot.
shocks
springs
complete bushing package
Figure some headroom in there and I'd say for $700 to $800, your Supra will handle like you never imagined. If your budget isn't so high, I'd do the bushings first. You'll notice a world of a difference right there, as your current bushings are probably old, rubber units. As for springs, Eibach or Dobinsons springs seem to be pretty decent. KYB or Koni shocks are pretty good, but I've heard unconfirmed bad reports about Tokico.
Hope this helps
(note: 935 Motorsports is a reputable seller as far as I know and from what I've heard, and they sell lots of Supra/Cressida stuff. I used 935 just as a guide.)