Hey, I would like to know what brand of strings and what gauge i should get put on my guitar. I mostly play metal, metalcore, death metal and such, and I'm almost ALWAYS in Dropped C tunning, and sometimes I wish I could play in B, but the strings i have right now barely let me play in dropped c, since the thicker strings are really loose, making my playing uncomfortable. Thanks in advance.
Some good brands are: Ernie Ball, D'Addario, GHS Boomers, Rotosound, Elixir, Dean Markley.

It's really a matter of trying them out. For every person you find with a bad opinion of any of them, there's another who has a good opinion of them.
D'Addario's have a rather woody, earthy sound when u first put em on. I have Ernie Balls on my guitar right now, but i need new strings. Id say GHS Boomers, maybe .11 gauge. .12 maximum for Drop B.
oh and another question. Would I also need to get someone to adjust the truss rod and bridge if I switch to a lower gauge strings ?
If you're only going from .10s to .09s or .11s to .10s, then probably not. If you're dropping from .12s to .09s, then probably the truss rod at least.