Heritage Auction Galleries is one of two sites in my Top 10 Best Coin-Related Web Sites that are alternatives to eBay. You will never be ripped off, scammed, or knowingly sold fakes on Heritage's ongoing online coin auctions, and sometimes the deals are amazing! One of my favorite ways to spend a lazy Sunday afternoon is to cyber-cherrypick through Heritage's wonderful, clear, huge images, looking for the overlooked minor doubled die, repunched mintmark, or other variety.
As if current auctions weren't enough, Heritage has a free online archive of more than a million coin images! You can do price research, grade comparisons, you name it (heck, I could almost write a whole tutorial about the ways to use Heritage's Web site!)