I don't have too much experience with buying lights for my bike and I need one that will illuminate my path pretty well in twilight/early night but I'm not going to be doing any hardcore night trail riding
I don't know how much you plan on buying, but you can buy lights that have a generator that spins against your front tire. Then you create your own light whenever you ride if you engage the generator. Here's an example, look at the front wheels at the top of the fork
or if you don't like spending that much...i personally just use a 5 LED blinky light. it lights up about 10 feet in front of me, which is all i need, since most of my night riding is in the city with street lights. it's mostly a "to be seen" by motorists light.
blackburns are nice as a reasonably affordable light, cateye makes really nice cheap ones as well. and just toss a knog frog on the rear, they're 12 bucks, and that way you are within the legal limits, if only barely.
once you go nightrider, you never go back, but as far as affordability then yeah blackburn, i use the nightrider moab for night intense trail riding and nothing beats it