Seco/Carboloy makes shell mills that take ISO APKT inserts which machine in aluminum very well.

I work nearly exclusively in aluminum, and with the right inserts these types of mills will make a mirror out of 3/4" bar stock. Very nice tools. They also have a 0 deg lead angle, so you can profile and rough with them too if you use the right inserts. Very versatile. I've got them from 5/8" all the way up to 6" in diameter, and they all perform very well.

I bought most of my Seco bodies on Ebay, for next to nothing, but if you want to buy new, I'd suggest going with a decent import or a no-name made in the usa brand.

Here's a 3" import over on Enco's website:
http://www.use-enco.com/CGI/INSRIT?P...PMPXNO=7909129

Inserts for these types of mills are very easy to find all over. You can buy the super sharp uncoated aluminum finishing inserts on Ebay for $7 ea all day long, and they will be quality inserts.

Travers Tool (www.travers.com) and MSC will have the name brand and the no-name bodies. I'd look on Ebay too. For inserts I never go anywhere but MaxPro tools. They manufacture their own inserts and sell direct, as well as on Ebay (which is where I found them). Very good prices, usually less than half of what MSC or even Enco wants for the same insert.

EDIT:

Here are a few nearly identical tools from MSC:

Ingersol:
http://www1.mscdirect.com/CGI/NNSRIT...53116&PMT4NO=0

Similar Import:
http://www1.mscdirect.com/CGI/NNSRIT...30236&PMT4NO=0

OMT:
http://www1.mscdirect.com/CGI/NNSRIT...64410&PMT4NO=0

That's just five mins worth.