The most popular home use mill to convert to cnc is the Seig X3 sold by both Grizzly and Harbor Freight (as well as some others). There are several kits to do it yourself, as well as tons of info on Cnczone from users who have done so and are producing parts that far exceed the tolerances required for our parts.
If you want a mack-daddy rtr cnc setup that is still single phase powered so you don't have to mess with phase convertors or have three-phase power, then the
Tormach and the
Industrial Hobbies machines are probably the two most regarded.