A tuner (planet waves chromatic pedal tuner (the £40 one)) or a noise gate (Boss NS-2, more expensive at about £60).
I have a bit of noise inbetween playing, but i also don't have a means of tuning apart from using the computer.

Thanks all.
Epiphone SG-400 (w/Hot Slags)/Chapman Guitars ML1 > Digitech Bad Monkey > Blackstar HT-5 > Danelectro Fish and Chips EQ > ETI Chorus Flanger
Snark Headstock tuner!
If you're getting an excessive amount of noise and its getting on your nerves, i would get the Noise Gate as long as its a QUALITY one.
Go used and get both.
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A tuner is definatly more required most of the time.

I've never felt the need to own a noise gate.
"In modern music, a lot of people are really stuck on the example, asif it were the idea. It takes millions of examples to articulate an idea, so don't get stuck on the f*cking example." - Joshua Homme, 2008.