Kensington, Tor/Forge, Dorchester and Medallion will also accept submissions with out an agent, but a lot of places won't. I tried to get an agent for about 5 months, then started querying publishers, including the above, and had much better results. Within 2 days of getting an offer I was able to get an agent. Have to say that my agent can get me in places I couldn't get before, knows a lot more than me about what's going on in a contract, rights etc., acts as a nice buffer between me and the publisher, negotiated with a lot more force and confidence than I would have, knows the big houses and their editors personally, and what they're looking for, and gets answers in days and weeks rather than months. I know in theory you're supposed to do it the other way. Get an agent and then get a book sold, but it worked the other way for me.