Miniature bases are not something that I will make a fuss about. I have bought plastics from various manufacturers, wood discs from craft stores and of course, metal washers. Plastic is my preference but if it is 30mm round or 25mm square, it will probably do. Occasionally however, the search for bases leads to a genuinely cool find.
I stumbled across Proxie Models on eBay, but their webstore is just as good and probably better for the company's return on the dollar. The bases themselves are black and with a slight textured surface. That possibly helps material adhere better to the plastic, or it may just look good. A $4.50 package contains four sprues of eight bases. Added bonus - the round center sprue makes a good stump or log for terrain builders.
The bases have a slight lip, which is convenient if you are adding some kind of basing material. I like a mixture of fine sand, latex caulk and paint. The base edge creates a nice border which holds the material better than a flat base.
Their products are made in the USA and shipping speed is excellent. I have placed two orders with them so far, and my bases arrived in less than a week. They also have some 28mm modern/futuristic terrain, including a pre-fab building that makes me want to play Fallout 3 with miniatures.