Ireilly. Does your
LFS have a "All the L-Numbers" or "Most Beautiful L-Numbers" book by Ulrich and Wolfgang Glaser? This is a great resource for looking up Loricariids (plecos all fall under this large taxon). I've been using
LFS's copies for a while, and finally bought a copy myself. It's a great resource to have.
Truth is... though plecs are very popular, they're still in many ways poorly understood and documented. And all the genetic variation between the strains (I won't say species, because a lot of species are contested or as yet unclassified) makes it very hard to determine what kind of plec you have. This book is about the most comprehensive resource for this, though.
Some other suggestions: Mega Clown Peckoltias are amazingly beautiful. If you can land a specimen, try. Queen Arabesques and King Tigers are astoundingly marked--labarynthine lines extending over the entire body. Gold Nuggets add wonderful color, and are a little more affordable than most other spp. Some of the bushy-bristlemouth variants are quite repulsively ugly, but others are incredibly cool. Look these up. I've seen one of these referred to as a "Medusa" or "Medusa-head" pleco. I think these are quite neat, and they have a more diamond-shaped body than your average plec. Some of the Pleco auctions on
www.Aquabid.com are a good way to aquaint yourself with the rarer species.
One caveat: a large number of Plec species/strains are nocturnal and marginally diurnal. I think you'll find that all but the common plecs and some of the bristlenose plecs seldom show themselves during the day. For me, this is the most exciting part about my Queen Arabesque (L-200) and Quasi-Snowball (L-142). When I see them, I really appreciate their presence in the tank. I never tire of them this way.