1981 Delorean DMC-12 - I know they're underpowered, but I've always wanted one since I saw Back to the Future. I wouldn't do anything custom to this until I got more money, but if I ended up with more than a million somehow I would probbably do something to beef up the engine a bit.
1971 Datsun 510 - This car would get a SR20Det conversion and possibly a widebody kit. Upgrades all around and I would do a severe weight reduction on it. This would be my SCCA car.
Dodge M37B1 Power Wagon - This truck would get upgraded with a swivel-frame conversion and more power, probbably a Hemi of some sort. I'd also add some basic creature comforts and it would get a fresh military paint scheme.
1958 Caddilac Eldorado Brougham Hardtop Sedan - In my opinion, simply the best looking 4-door sports sedan ever made. This car would get the exact same paint as the pic. I would upgrade the engine with a supercharger to give it more oompfh, and modernize the suspension and brakes, possibly lowering it a little bit to make it handle better. I wouldn't turn it into some stupid lowrider though.
MKIV Supra w/ 99 Veilside Limited Bodykit Link2 Link3 - This would be my baby. Most of my available money would go into this car. I would probbably buy the body kit and then have a whole custom copy of it made in carbon fiber. The engine would get your standard 1000+ hp treatment. The interior would be custom carbon fiber all around. The door handles and all emblems would be shaved. The car would be painted in the deepest black I could find, with
these wheels. Everything about this car would scream speed. I would make this as close to not-street legal as possible. It would be a one of a kind vehicle that would set the standard for custom supras.
2004 Toyota Prius - This would be my daily driver. I would load it with every option available, throw some rims on it and upgrade the stereo, and that'd be about it.
All these cars except for the Truck and the Delorean would be black on black. Any money left over would go into a lift and tools to work on them. The garage would be climate controlled and would have a decent stereo and a fridge to keep beer in.
I don't think I went over a million, most of the cars would be relatively cheap (in millionaire terms) except for the supra, which as described would probbably cost at least $500k, probbably more.
Edit: Fixed links, i hope.