There are a number of companies that have made a board with both an AGP and a PCIe 16x slot. But you have to be careful when choosing, especially for the AGP side of the deal. A few of these boards have actually bridged their PCI slots so an AGP card fits in them, but the bandwidth is incredibly low. Not a true AGP slot. If you are trying to run a high end AGP card, it will be heavily crippled by the low bandwidth.
The Asrock dual (the one Howard has linked to above) seems to have the best reputation for this type of board, and from the benchmarks it's performance is quite impressive both on the AGP side AND the PCIe 16x side.