newbie, single speed crankset brand and teeth count
 

I'm new to single speed. I have a mountain bike that I plan to convert. What are some of the common brands on crankset? What about the teeth count? I will be using this for commuting, mostly flat.
What are some crank-cog combo people usually use?

I used old 170mm Shimano 600 cranks on my MTB and had to change for a longer BB. I ride 47x17 on 126x1.2 which gives around 67 gear inches. It's a nice ratio for a beginner (like me).

Crank brands really aren't that important especially for a first conversion.
Just make sure the crank has removable chain-rings.

I currently ride a 28/13 ratio on my SS MTB aka Over-sized BMX :)
That gives me a 2.154 : 1 ratio.
I'm usually sprinting though.

If you're going to be commuting, you'll probably get skinnier tires.
Try something like ...
2.3 - 2.8 : 1 ratio.
Fiddle around with chain rings and cogs. That's the fun part.

Ratio = (#teeth on chain ring / # teeth on cog)