I just purchased a PA. I used an audio-technica MB1000L to mike the guitar cab and it didn't pick up much of the sound.

Which mike/s should I go buy?

is that an instrument mic. i mean just for mic'ing a cab in a live situation the shure sm57 are great and can be had for cheap. probably $50usd used
Gibson 58 VOS, Gibson Rich Robinson ES-335, Fender Strat, Fender RoadWorn 50's Tele, Gibson LP Jr Special

Marshall JTM45, Fender BJR NOS
Any chance it's not the mic's fault? You're not giving us exactly a lot of info here. What is the problem, precisely? Do you not get enough volume? Is the frequency-response too limited?

The MB1000L is a dynamic mic, which typically is what you want for stage use.
I'm not getting much volume at all.

When I speak into the mic it's very loud.