The Tropical Isle in Natick has just about everything to do with aquaria, they are very pricey though.
Also, I just recently checked out Uncle Ned's Fish Factory in Millis. He stocks alot of cichlids.
I just found out about this place yesterday! I went there today and if you are into saltwater aquatics, this place is great. They have a good selection of freshwater too. Prices are good and the quality of fish are great. Good sized shop located in Auburn, ma. http://www.krystalclearaquatics.com/