Whatever you can get used, or whatever you didn't sell from your last upgrade. For those with bigger tanks there is also the "borrow one from the display for a month" option, although that gets old fast.Much the same as fuge lights actually. I went with a used black box for a while (it's dying, but not entirely dead yet). In a pinch I've also used an old T5 that I have. Looks silly putting a 5' light on just about anything other than a 5' tank, but hey, it works.You can often find used 250 W halide pendants at some of the LFS in the used section with a ballast and working (albeit old) bulb for under $50. Be careful to keep these high, I like to acclimate most new frags as if they came from a low light situation.
Thanks for the input!