I have a lawnmower blenny that has great personality, he;s great for algae eating and is always follwoing me around watching. lol You could also go with a watchman goby/shrimp combo too.
Check out liveaquaria.com they have the best information with requirements and the such.
I have one blenny and one goby in my 55g. Just stay away from mandarins and scooter blennies, they don't eat prepared foods really.
I learned the hard way. lol