I was reading through the replies you guys have given and to tell you the truth I wasn't satisfied with really any of them. Tempo really doesn't relate to any of these genres. I'll start with the basics that I have learned from reading web pages dedicated to informing readers about different genres of electronica.
Techno - Like someone else said...it can tend to be fast paced melodies but you can't always write a genre off and solely that. There are many variations and saying that it is always fast paced isn't accurate. Genres in my opinion are generally categorized by the kinds of synths used. Like someone mentioned above...dimrain47's work is a great example of techno.
Trance - Someone said trance is usually around 120 - 140 bpm. that's not necessarily true either. Although most of the time that is true, it can be faster when it's happy hardcore (sub genre), and then it can be anywhere from 140-180 (estimate). Trance uses alot of repetition of sounds, repeated melodies and things like builds. Trance tends to use alot of snare and crashes. Trance can feature very melodic vocals as well. But then again there is also hardstyle trance that is more "dark" if you will. Using more trancy sfx rather than melodies.
House - House has a very tricky beat most of the time. Rather than kick kick kick like trance, it is more than likely to be kcik kick kick ki-ki-kick or something along those lines. From what I've experienced it can use more sine or crunchy synths or 'nasally' kind of like that i guess.
Dance- Dance is like trance but kind of without the trance haha. I don't know too much abotu this genre.