MH lights are best for veg, HPS best for flowering, but unless you can find a good deal on a dual spectrum, i'd say its best just buying a HPS light (but it depends how serious and how much youre willing to invest) wattage depends on how many plants your growing, and how much space you got, 250w hps is the smallest i see, which will grow a few plants, but the more powerful light the better yield youre going to see.
remember ventilation is JUST as important as light, especially if youre using anything over 250w, and in this summer its mad heat..

for sites well theyre not too hard to find, i know UK 1's but i think youre from usa.. can get some good deals on ebay but i'd have them delivered to a different house from the grow from what ive heard..