Hey homer. I work at a house club so let me give you some good suggestions.
First on rap. If you like Wu Tnag and such you really should check out Kool Keith/Dr. Octagon/Dr. Dooom, it’s amazing stuff. I posted some of his lyrics in the rap thread in the pit.
House tends to be slower and lusher than other forms of dance music. You get more vocals, more instrumentals and such. You have things like Brazillian house, deep house (tends to be slower and sexier), tek-house (faster and more machine like), gabba house, and other varieties.
Techno is stripped down electronic dance music. More on beats and samples. Tends to be faster. You also have the crossover tek-house, detroit techno, etc.
trance can be really bad or good. Trance music tends to be more dreamy and drug like. You have progressive trance (heard frequently in clubs; paul van dyk, Digweed, sasha); cyber trance (which is closer to techno and has lots of cool beats and samples), psychadelic trance (which is more druggy, one DJ halucinagen tends to mix in pink floyd songs at intervals); goa trance (which is faster and kinda like a mix of techno beats with trance sounds),Hard Trance, and etc.
Drum and bass. Fast heavy beats lots of snares, good music for alcohol consumption. This uns the gamut from atmospheric (very romatic, good for sex), dark-tek( darker more disturding), 2-step (which is the newest form, very funky pretty cool, see if you can’t pick up some 2-step stuff), etc.
Down tempo is what it sounds like. Good chill out music
And ambient.
Of course I’m forgeting all sorts of stuff here.
I suggest you go to the following site. http://www.thump-radio.com
They have all sorts of amazing international djs broken down by catagory. You can listen to the music, decide if you like it, and then go out and get music of that genre. Try out Mystre, Zoo-b, Galen, Mars, Hallucinagen, Tracer, Andy Sine, Digweed, Dutch, Garvin Hardkiss, and others. The ones I listed are a good cross section of some of the various musics.
Some good DJs to pick up in stores.
Digwwed, Kimbal Collins, Sasha, Darren Emmerson, Medicine Drum, Dj Dan.
Hope that helps Homer. Let me know how it goes.