Like others, I have many sources. Actual books I have Lee, Lyman, Hornady, and Hodgdon (yes, I bought their "magazine" reloading book) plus I downloaded (and printed) Western Powder (Accurate) and Alliant Powder's online PDFs, plus I downloaded various bullet manufacturers online data (Speer, Campro, Nosler, etc) plus I downloaded older copies of IMR (2003?), Winchester, manuals etc. Seriously, there is so much information out there (oh ya, I also have a subscription of Loaddata.com!)
Then for each caliber I reload I have a Google Docs spreadsheet that lists the projectiles I have, powder I have, and the high/low from each reference source. This summary page is my go-to and any load that is noticeably higher or lower on the powder charge is (to me) discarded and I try a variety of loads as I "work up" to something my firearms like.
I admit, I'm kinda crazy but I enjoy reading and rereading reloading manuals and load tables. Just last night I was reading up on loading 45acp for a Hi-Point carbine (currently have a 1911 clone that I shoot 200gr plated or SWC with Bullseye powder. Wonder how those rounds will work in my new-to-me carbine).
All fun!