This playground article on digital multiplexing [Arduino Playground - MUX151] is helpful. One problem: I can't find 74XX151s anywhere (octopart, mouser, newark).
Do they go by a different name? Anybody know where to get these?
Remember that the "XX" in the part number is not a literal "XX" but aplaceholder for whatever type of TTL chip you want. So, the actual part number could be 74151, 74L151, 74H151, 74S151, 74LS151, 74F151, 74ALS151, 74HC151 or 74HCT151 (I've probably missed a few!). But the difference only really become significant in high-performance circuits, or for making exact replacements of existing chips. You will probably find that the commonest types today are 74LS151 and 74HC151 (for Low power Schottky and High speed CMOS). Either of those types should be fine in an Arduino circuit, and the 74HC151 will most likely have lower power consumption.