I just use a Wahl kit - but any will work - I can trim my hair and beard in one shot. If you want a different length (the plastic guards) - you can buy other sizes (longer and shorter) at any "Beauty Supply" Store. (Sally's is a common one)

The secondary trimmer comes in really handy as well, and runs off a AA. (I feed it a rechargeable)

http://www.amazon.com/Wahl-79524-5201-Chrome-Complete-Haircutting/dp/B00827ILWM

(I bought the same kit at Target)