I think I need new brake pads, since they are starting to squeal.

Any suggestions on what I should do for replacements? Are OEMs good enough/better?

Seems like people are saying that OEM's are good enough. Also, I'd like to get rear discs. How much do these run?

 

for "regular" driving, or even decent performance driving, OEM brakes are some of the best you'll find.

you can spend more and get Axxis, porterfield, or EBC pads, but if you don't do any REALLY hard driving, you'll never justify the extra money spend.
OEM brakes will get you from a 100-0 stop in short order. jsut don't expect to be able to do them all day long without fading. (no oem brakes can do that- unless you drive a porsche or ferrari. Stock M5 brakes won't even handle a lop around a tough road course!)

 

OEM pads are a good choice. I've tried some not OEM that are considerably worse than OEM for many reasons.
Good luck,
DDD