Depends what kind and what price range you're looking at. I have a Turbo Tuner, but that will set you back about $130. Just go to a local guitar center and have a look around at something in your price range. Can't go wrong with anything by Korg really. Whether it's their $70 pitch black tuner, or the cheaper $20 ones.

Either you want a pedal, or just something you can plug into for practice use. For a beginner, that's all you really need. don't need to spend more than $25. A little more if you want it to have a metronome built in.

http://www.guitarcenter.com/Practice-Accessories-Accessories,New-Gear.gc
http://www.guitarcenter.com/Korg-GA-1-Guitar-and-Bass-Tuner-105473219-i1449479.gc
http://www.guitarcenter.com/Korg-TM-40-Digital-Tuner-Metronome-103240545-i1125538.gc