It depends what you want and what kind of skill you have. Take a look at STI and Caspian for slide/frames. For internals you can go dozens of directions. Everything you need you can get from Brownells or try Shooters Connection. The nice thing about Shooters Connection is that you can call or email, tell them what you want and they will tell you what you need. If you talk to Shooters Connection, make sure to let them know that you don't want a "race" gun, just a shooter (unless you want a race gun?) Their prices are very competitive but their return policy isn't real great so be aware of that.
Now, a 9mm in a 1911 can be finicky. Even factory guns often need a "tune up" from a good smith to get them running reliably. Don't skimp on mags, buy the best you can get. I would start with Tripp Cobra's. Someone made a suggestion of a .38 super which would be a good choice too but ammo can be much more expensive and brass is harder to find and more expensive (if you reload).
Oh, and if you decide you just want to buy one and get it overwith, take a look at STI's Trojan. Dawson Precision had them on sale for just over a grand this week. They are forged parts (I am 99% sure, anyway) and for that price you can't buy good parts and put it together yourself. The only thing I don't like about the Trojan is the stupid STI logo on it. You can buy a total "bald" slide with nothing on it and when finished they look pretty nice.
I am currently getting parts together for a .40 but I won't do the work, I ship it out. I am kicking around a 9mm next though. I think a well put together, running 9mm, in a commander frame would be the ticket for concealed carry and just plain fun!
