APMEX in Oklahoma City is a long-time reputable firm which sells and buys bullion coins. If you are relatively nearby, going there yourself is an option. Otherwise you can sell to them by shipping it to them, insuring it, of course. I have dealt with them for years, and have complete confidence in them, as they are the largest such operation in the US. And they pay a reasonable discount from spot.
If you are selling under $1,000: Open your yellow pages, look under coin dealers, call the biggest dealers and ask their buy/sell prices for your type of bullion in relation to spot, carry the metal to the best dealer. If selling over $1,000 it is probably worth your trouble to mail the metal to a larger out of town dealer who will give slightly better prices. Check out Tulving.com - he is hard to beat but is also know as the soupnazi of dealers. Another of the lowest overhead dealers is golddealer.com - check around online, call numerous dealers, and you will save a few bucks on a large sale.
If you go to a pawn shop, jeweler or coin dealer, you are an idiot. You will get ripped off. APMEX is decent. Bullion direct is better. Then there is craigslist and Ebay. Alternatively, send me a PM, I might be interested in what you have.
I second what lorax has to say above. In the last few months I've found that coin stores are willing to pay a premium to spot for rounds and small bars, just ask around. Remember that with Craigslist there are issues with trust and shipping, and with Ebay there are the fees which can be almost 10% if you also use PayPal. Do a little shopping around and don't accept a large discount to spot.
I would love to know the names of some coin stores which will pay premium to spot for rounds & bars. I doubt that any would pay a premium for bars, as their standard operation is paying spot for name brand CME accepted bars and discount to other brands. Only way I can see premiums for rounds is for ASEs, since the standard premium for those runs at $3-$4/oz, so I can see a coin store offering $1/oz over spot. If you have standard acceptable silver (or gold) bullion & generic coins, Bullion Direct is an indicator of fair market value. I have yet to see any physical coin store, jeweler or bullion dealer come close to that. Hence, my comment of ripoff.