I have a 3 gal as well. As far as fish go, I am not going to add anymore ever again. I had a clown goby but don't know where he went, cannot find him on the floor so maybe he died. I just don't have luck with the fish and in my opinion the 3 gal is just way to small for any kind of fish to be really happy.
My tank is now an invert only with some coral. I think its full enough and interesting with what i have, although I would like to add a porcelain crab but still doing some home work on it.
Here is what i have in my 3 gal:
2 sexy shrimp
1 pom pom crab (never see him but sure neat when i do)
1 cleaner shrimp
1 algae eating cowrie
1 snail
1 hermit crab
orange florida rics
purple florida rics
green star polyps
reg button polyps
small frag of zoas
anthelia
I would like to add a nice pink or yellow dwarf feather duster for that punch of color when i can get one.