Depends on how much you wanna spend! I love my Innova 18" by ABM International (made in Texas!). Since I could write a book on why I chose this machine over any of the others...PM me if you want more information. Mine starts at $8,000 (I think).
http://quiltfrog.com/ sells many brands and they are having a sale now.
http://www.quiltsonthecorner.com/ Has a wonderful free article on shopping for a longarm - center of the front page is where you'll find the button, and you shouldn't have even scroll down!
Not affiliated with anyone, just did a little hunting on the internet!