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There are many of them with ADCs. Just one example the LPC900 family from Philips. Small micros with 8-bit or 10-bit ADCs.
How many inoputs do you need? The LPC935 has 8 times 8-bit inputs, the LPC938 has 8 times 10-bit inputs.
For pricing you can have a look at Digikey. **broken link removed** then search for LPC9
The best ADCs on a 51 you can get from Silicon Labs or Analog Devices but they are much more expensive.
most of the lpc seris ic's have a inbuilt adc & dac converters. not one but 4-8. these ic's are of low cost & less no of pins. may be u can have a search on the philiphs site for 89lpc9xx series of micro controlllers.