I've recently come across two sites offering some interesting accessories for my D&D games.
First on the list is Dapper Devil. They offer colored bases for D&D miniatures, in various sizes and colors. I think this was originally intended for use with the D&D skirmish games to help identify one person's minis from another.
In addition to the miniature bases, the site also has a number of tiles that can further aid in a game, from various status effect tiles to spells, and even treasure tiles.
For character tiles, or paper standups, there are a number of companies that make plastic stands, from Steve Jackson Games, to Fantasy Flight Games. But I've found a solution I like more than those two for a number of different reasons.
RolcoGames sells pieces that can be used for a number of board games. The one product that I like for my game are the game stands. They are available in a number of different colors and at 3/4" x 3/4", they fit within a standard 1" space. Again, I like the color variety since I have multiple versions of the same creature with different color bases to track each independently. Also the price for these game stands is cheaper that the other companies listed.
If you use a lot of D&D minis or flat cardboard minis, check out these companies, I'm sure they have something you just might be interested in.