Sierra from a CD (has some oddball rounds and good interactive stuff)
Speer (current and previous edition)
Hornady (current edition)
Nosler (one edition old, like it for listing load densities)
Hodgdon Online (This gets the most use)
Random online suggestions (For some of the hard to find, or recently released)
I'd say I've never started loading without consulting at least two different manuals.
I dont relegate myself to just one. I use several and compare loads for bullet weights between them all. I kinda come up with a consensus opinion. I will give extra credence to the manual of the bullet I am loading however. I also use online resources as well. The manf.'s are getting wiser and putting a lot of their reloading data on the web now.