A shameless plug but I get all my USB->RS232 kit from Brainboxes, who use FTDI chipsets. I've also been trying their Ethernet to RS232 kit which is pretty good (it fools a 15 year old piece of software into thinking the VPN'd Ethernet box is a serial port built into the PC running it).

Mark
G68, baby Genelecs, Humax Foxsat, Oppo+Vanity93, Toshiba HD-A35, Pioneer CLD-925 + Meridian 519, various other random bits and bobs
Got a black G08.2 you want to sell?