I love the decimator prorackG.
2 channel, one for before the amp, one for the effects loop, and it takes your input signal and preserves that in Channel 2 so it's easier to dial out amp noise, 50/60Hz hum and any noise from other pedals.
A bit pricey, but I don't think I came across anything else that comes even remotely close to this when I was searching for noise reduction systems!
BTW Noise Gates are something a little different, and you probably want noise reduction instead (ie filters out the cr@p but leaves your signal alone).
Hope this helps,
Roo