Type O Negative is 6-string tuned down to B, so you could just use the 7 string for it.
I also recommend Nevermore. They're my favorite 7-string band.
Also, Fear Factory. Soul/Demanufacture era are standard 7 string tuning, while later
stuff is tuned down a step. The new album has 8-string shit on it (sounds like it's tuned down as well,
which would put it at F...which is just fucking silly
)