Hi,
Depending on what you want to do, and how accurate your 12bits needs are, the sampling rate of the device and how many channels you want, te accuracy of your internal reference.
All these are vital informations for the choice of a ADC, you can find 100s of different 12bits ADCs on the market that has the spec you mentioned here, but you can make it easer to search for an ADC if you have more precise specificaiton of your needs.
Take a look at Maxim, TI and AnalogDevices, other easy source of search is the DigiKey and Mouser in the US and Elfa in Sweden, they have a wide range of components that makes your search easier and ordering them much faster.
Good luck with your search,
/Farhad