As far as compatibility goes, you just have to make sure that the impedance of the speaker doesn't dip below, say, 4 ohms depending on the sensitivity of the speakers and how loud you want to listen to them. Low impedance becomes less of an issue as the frequency increases, but typically impedance will drop near crossover points (e.g. between 200 Hz and 4 kHz). You wouldn't be able to check this unless the manufacturer provides an impedance graph, or hobbyist/reviewer testing is done.
As far as what speakers to get, in general... how much money do you have to spend?