GCBasic won't make the grade, in the sense that no USB library exists. Porting a software USB would be a lot of work, and not sure possible? Swordfish Basic has a USB library, but I think you have to have the paid version.
Using a FTDI FT232RL of course works great, all the Arduino boards out there can't be all wrong. Microchip finally came up with the
MCP2200, which is a USB to UART chip. Don't know all the details, but sounds promising, and cheap to boot.