Craigslist is the devil, but a great tool for selling. I prefer it over ebay.
So far I've bought a 75G, 10G, 5G and 2.5G all off craigslist. I'm waiting on a shipping price for (2) 2215 Eheim Classics from a guy in Florida.
If one wants to search the entire site and inquire about shipping or maybe they are going on a trip and can locally pick something up, go to
www.google.com and type the following "aquarium site:craigslist.org" in the search box and click search. It will search the entire craigslist.org site for aquarium. Change aquarium to whatever you want to search for.