I'd agree with the 3208 - its available in DIP and surface mount, and works at 3.3V as well as 5.0V, and gives 12 bits and is faster than built-in ADC. (You do need to use 4 pins, but 3 can be shared with other SPI bus devices).
Analog multiplexing chip might be a little cheaper though (still needs some digital pins to address it though, which would be harder to share with other devices?).