I find ebuyer to be reasonably priced and if you haven't come across their site yet I have included a couple of links for both the pcmcia card and USB options. The customer reviews are always useful with links to updated drivers and ways to overcome common setup problems etc.
http://www.ebuyer.com/UK/cat/Sound-C...al-Sound-Cards
http://www.ebuyer.com/UK/product/90815