Ok everyone- a brief history; I have been raising Cichlids in the past and my wife has been asking for a marine aquarium for our livingroom so I'm in the process of getting equipment together for it. So far I have a 55 Gal and stand; canister filter, and protien skimmer. It will take quite awhile before it is up and running.
In the meantime, a neighbor just gave me a 20 Gal (long). I posted on the cichlid forum for stocking advice on such a small tank. I got some great responces but since then, 2 co-workers and the LFS owner have suggested starting a marine tank (practice they say for my 55). All 3 have extensive Marine tank experience (one even has a 20 Tall in his office). They all will donate live rock and other needed items (water and experience, etc). They agree on most things except on type of fish. What I would like is some advise on stocking this tank (if I indeed do a Marine tank). This will be going in my office and I need to do it "on the cheap"; cheap hardy fish. I dont mind having a single specimen tank so if thats my only option its cool.

Thank you all for you help!