It's a Pseudotropheus of some sort (also and perhaps more properly known as Maylandia or Metriaclima depending on who you're talking to). Most of the cheap ones in pet shops are Pseudotropheus zebra based hybrids. A little time thumbing through a decent Malawian cichlid book may help you pin things down a bit, but if the pet shop doesn't know the species, assume it's a hybrid and act accordingly. The Malawian cichlid hobby has been ruined by hybrids, unfortunately. One problem is that a hybrid won't conform to type in terms of size, behaviour and colouration, so you really can't be sure what you're getting.
Cheers, Neale