I use a compination of harmonics and fifth fret rule, usually whenever I'm not quite on pitch. Harmonics are useful because they're what's been called a "pure note", i.e. there's no possible thing to prevent them being the right pitch (aside from intotation...)

Whenever I tune with harmonics I tune the OPEN b string with the 7th fret harmonic of the E string. I find that's the easiest way. The only other option is to tune the top e and then tune the b to that. Just a few ideas, I'm sure there's a better way...Hope I helped though