Snark SN-8 Super Tight All Instrument Tuner
A clipon tuner will make it much easier to stay in tone though you can get apps for your phone that work pretty well. If you're having problems practicing because you fingers hurt, you may want to try tuning the guitar a half step down (there is a setting in the tuner or app). This will make the guitar sound deeper but will also lose up the strings a bit.
