well all depends on what your into...

american: V8 camero/mustang... many are POS and sound better then they run, but if built your talking real power that most imports can't touch... if you want 4 banging SRT4 stgIII or SVT Foci + boost

european: S4 debadge to look like A4 makes a great sleeper, or 1.8t + turbo upgrade (way cheaper and practical )

japanese: s2000 + boost, vr4, rx7 + boost, specV + boost, any hondoh!...