It really depends on your requirement. I can provide you few suggestions.

If you need Low Speed sampling but you wanna reject 50/60Hz noise you can use MAX11213 (Maximum 120sps) - SPI based

If you need a mid-high speed sampling you can use MAX1169 (Maximum 58Ksps) - I2C based
OR MAX1133 (Maximum 200Ksps) - SPI based

If you need real-high speed sampling then you can use MAX19588 (Maximum 100Msps) - 16bit Parallel interface

The good thing is that in most of the above parts you won't need any external peripherals like reference or clk source. These are all built-in.