A good point to start could be the Analog Devices web sites: search for data sheet and app notes regarding their DDCs (AD662x and AD6636).
See also Texas Instruments and Graychip but I don't know nothing about their DDC (if any).
Mowgli
Hi,
Are you looking for direct digital downconversion or simply downconversion. Direct is a hot topic and AD has used it in some of their projects also some RF companies RFMD (I guess) has used it commercially.
BRMadhukar