As mentioned elsewhere on this site the Si570 is offered in several variants, covering from 10MHz up to in some cases 1.4GHz. it is tuned via the I2C interface, and can in some cases be tuned down to about 3Mhz. I have seen many people use it as a local oscillator for Ham radio projects and such. The only thing is they are a pain to procure right now as the part is fairly new.
this part would make an awesome addition to those inclined in designing their own hardware for use with the existing GNU radio code base.
N2TOH