Bitcoin is an absolute must, of course. You might also want to consider Doge (their community is fantastic) and Litecoin. Another possibility would be DASH. Of all the "Dark" coins, it is the user friendly and widely held.

Before you decide however, check to ensure that the coins you choose are relatively stable. The last thing you want to do is accept payment in a coin that crashes before you have a chance to exchange it for Bitcoin or fiat.