All of the above plus one more online source, Alliant Powder - Home, it's just for alliant powders, but there's a lot of good info there that's not in a lot of the other manuals mentioned above and they make many good powders.
I use multiple manuals, the web, and keep my own hard bound records of loads I have tested. Just keep in mind that the data in any manual was developed with specific components in a specific test barrel with a specific lot of powder. Over time manufacturers may make changes in the components thus the difference in loads from a 20 year old manual vs a current one. Also, different lots of the same powder may have slightly different burn rates. Thing of how many powder companies have changed hands in the past 40 years!
As most have stated, review several sources and start on the low side then work your way up (if you need to go up) and you should be good to go. Make sure you understand the signs of excess pressure before you start.
The longer you load the more books you will buy as it becomes a deep obsession. I just got the Berger book and had a great front end read. It is rifle only. I will say I do like the Sierra book too. Have the Lyman, lee, and one other that I can't think of now. I have my dad send me images of his hornady book. I have searched to net, asked on forums, and all kinds of things to search data. You will want many resources as you get into differet bullet and powder combos.
When I bought my first .327fedmag a few years back, the interwebz was the only place I could find data to load for it.
There are still few manuals that include it, but data is getting easier to find.
I have the Lee Modern reloading, Lyman 49th, Lyman Cast bullet handbook, Hornady's Handbook of cartridge reloading, a couple of older Speer manuals that were given to me, and several annual Hodgdon magazine style manuals.
I also have several sites bookmarked.
You can never have too much information.