Having had one myself a couple of years ago, I don't think you can go wrong with an E36 M3. You can either pick one up for less than 20K and drop a supercharger/turbo kit in it, or just buy it as is.
1998 BMW M3, 6 cyl, 5 spd, ps, pb, ac, p/seats, pdl, cc, stereo, am/fm, air bags, abs, sunroof, supercharged 400 hp, lthr, tint, alarm, front cover of BMW Car Magazine 1/06, $30000
Although I know over here (US) you only get the 3.0ltr one, I was in the BMW drivers club in the UK and a couple of people had twin turbo E36 M3s, to say they left my standard M3 GT Limited (basically an M3 Evo with lightened parts for track use, they only made 50) for dead was an understatement.