I highly recommend these little guys: http://liveaquaria.com/product/prod_...pcatid=164&N=0
I have had nothing but success with Rainford Gobies, and in my experience, have been one of the hardiest species available.
A Rainford was the first inhabitant of my second nanotank.
He went in the first week after I set up the tank and he's been healthy and happy for 5 months now.
He even survived a "chemical accident" that took-out most of his tankmates.
(I forgot to wash my hands before sticking them in his tank and must have contaminated the water with some testing solutions.
Rough way to learn my lesson...)
I've been thru a few other goby species and some blennies with no luck, but so far all 3 of my Rainfords and my Diamond goby have all done wonderfully.