For your main filtration you have: HOB, sump, and cannister filters. I have already stated why I dont like HOBs, and the same problems can be true for cannisters. You can do either one, but you have to be on top of cleaning out the filtering media. I reccomend a sump. There are many more options with sumps, like including an algae turf scrubber and a skimmer into the design. Along with the ability to include more biomedia as well.
I reccomend an algae turf scrubber. You can build your own, and they are cheap. There is a how to on this forum that I can link for you if you are interested. You can compliment this with a protien skimmer if your budget allows. I sort of reccomend you do a skimmer anyways, since the turf scrubber and the skimmer serve two different purposes. A skimmer removes un-used nutrition before it can break down into nutrients. A scrubber removes nutrients. For clarification, nutrients are to mean nitrates and nitrites, which nutrition is basically food/waste.
Lighting is going to depend on if you are doing a fowlr or a reef tank. Fowlrs dont really have any light demands, so its up to you. Corals, depending on type, have varying light needs, but the most demanding type should be catered to. I think for a tank of that depth, a 4 bulb t5 fixture that spans the largest dimension of your tank is good enough for coral keeping. Aquatraders.com has some good prices on their stuff, if you go elsewhere, you will pay an arm and a leg.
You will want some power heads for water circulation in the tank. I think (2) koralia 2 power heads will do it. I reccomend that brand because they are well made and cheap, but the choice is yours.
If you are interested in building your own sump, glass-holes.com has some nice kits to put in an overflow, and I can dig up some tutorials on how to build a sump. Its very easy, and I think a 20 gallon sump would be more then enough for a 45.
I cant really comment on skimmers and brands because my product experience is really limited. Someone else would need to pipe in.