Favorite ADC?

I'm designing a shield to add I/O capability and am interested in throwing on some extra analog inputs, though I don't specifically have a project in mind that would use them.

I'm fairly new to this sort of thing and am interested in seeing if anyone has suggestions. I know ADC can be "tricky" and people are often careful about routing and noise protection. I suppose there are probably volumes written on the subject, but I'm just looking for a place to get started.

So, I'm wondering if anyone has a favorite ADC chip to expand the arduino's capabilities? If it ran on I2C, that would be swell.