Hey I play bass and haven't paid a whole hell of a lot of attention to electric guitars. I was just wondering if there are guitars out there with the low B string like 5 String Basses have.
Yep, lots. Seven-string guitars are pretty common in metal.
El Gearo:

Fender '69 Reissue Mustang
Fender American Standard P-Bass

Fender Blues Junior
yup, like RNRSoldier said you have 7 string guitars that come with a low B and you can downtune 6 string guitars and using heavier strings like a .58 for the low B tuning. UNLESS if your talking about having a Low B string like .130 then hell no....that would be WAY to damn thick for a guitar.
Crank your rig on 12, let it feedback wide-open for a good two minutes, freak your neighbors out and ENJOY THE POWER OF THE GUITAR! 'Oh, what a feeling,' and it ain't no damned Toyota!" ----Dimebag Darrell