I can only really think of The Right To Go Insane, I'm absolutely sure there must be others... Anyone? I'm considering looking for a 5 string bass (specifically the Ibanez SR505) but I wanna know if it would really be worth it and what songs could I cover to master the 5th string? Thanks!
for thrash, you probably wont need it, but for black metal, death metal, and anything in B tuning, it'll be awesome
Stumbled upon this. Not a comprehensive list but somewhat helpful: http://en.academic.ru/dic.nsf/enwiki/6738815

Thrash specifically? I believe some of Arch Enemy did some albums this way. At the Gates were not thrash, but were gods of metal and their songs are fun to play. Most thrash is played in E standard but I'm sure there's plenty of thrash bands that play with B standard tuning.
The SR505 is an awesome bass, but there's not that many thrash metal songs that use the low b string... maybe try prog dream theater?
Bass: Ibanez SR505

yeah dream theater is nice, but which songs could I play with only a 5 string bass and not a 6 string that would help me master the 5th string (as in, not extremely difficult)?
yeah well I don't know then, i started learning to master 5 string by playing prog, or testament cuz some testament is played on a five string and testament is thrash
Bass: Ibanez SR505

i had the same problem with my 5er i could never find any use for the B string.
so i will restring my bass with warwick yellow labels and go for the high C instead.
I know duality by slipknot and I play that in standard on my 5 string if that counts.

I've been looking around for the same stuff but can't really find anything good.
Random off brand P Bass (Fretless)
SR 485 Sound gear 5 string bass
60's Crown violin bass
Rogue RA-100D Acoustic Guitar
Peavey TNT 115 Bass Amp
Bass Big Muff pi
Dunlop Crybaby Bass Wah
some of Rob Trujillos work with Metallica is done using the low B, not exactly sure what songs though
My Rig:
Yamaha RBX 375 bass
Peavey Millenium BXP bass (won at Summer Slaughter 2010, signed by all the bands)
Eden Nemesis NC410 320w combo amp
Check out Tyrannicide, my death/thrash metal band:
Check out Carcass, they were one of the first bands to go to B and maintain a clear sound, not just a mess of noise.