#1
I'm using a Krank Rev Jr. as my amp, which doesn't sound terrible. However, for metal, it needs a nice overdrive to really get it into metal/shred territory. I've been using a VisualSound Jekyll and Hyde, but the amp's gain is fine (one of the better gain tones for under $1000, really). I've found that the Jekyll and Hyde is a bit too noisy and, seeing as I do not really need the distortion part of it, am in need of a new overdrive pedal.

But which one?
I play stuff like Megadeth, Racer X/Paul Gilbert, Dream Theater, and neoclassical (Yngwie, Jason Becker, etc.)
I have been looking into the Ibanez TS808 and the Fulltone OCD, but am really not that sure on which to buy.
#3
Make a list of several and go to youtube to see which you like best.
Dean Icon PZ
Line 6 Variax 700
Dean V-Wing
Dean ML 79 SilverBurst
MXR M 108
H2O Chorus/Echo
Valve Junior (V3 Head/Cab and Combo)
VHT Special 6
Phonic 620 Power Pod PA
Wampler Super Plextortion
Line 6 Pod HD
#4
You can get tons of differant options ranging from Maxon OD808 and OD9 which are really great because of the true bypass circuitry, then there are the standard Ibanez ones like the TS808 (which is pretty expensive) the TS9, and TS7 (which I have, great pedal. Consisting of the TS9's circuitry, and an optional "Hot" switch which is just more distortion).
Of course you can go with Fulltone as well which I hear are really great, and then there's the BBE Green Screamer, and Keeley modded TS's. Check all of those out on youtube. I didn't really like the Krank Jr.'s sound at all, but I didn't try it with an OD, so who knows.