the one i run i got from mechman alternators. 280 amps buddy mechman.com is there website. thats a big enough alty to run a system and hid kit and what ever else you need. but i always recommend adding another battery to vehicles with larger systems.
here is a pic of my old 250 amp alty from mechman......
next to the stock one lol.
installed.(tight fit)
i used this alternator and 3 group 31 batteries with roughly 16000 watts of clamped power in my competition truck.