Include books, blogs, websites etc. -- I am only including websites tonight ... I have to give the books some thought ...
I'll knock a few of the obvious ones out of the way early ...
NewAdvent -
Bible (with commentary),
Early Church Fathers,
Summa Theologica, 1917
Catholic Encyclopedia - Whats not to like? Well organized and easy to get around. Man, I didn't realize until today that New Advent had a bible with commentary. I may be up all night!!!
Catholic First - More ECF's, another online Catholic bible, CCC (all searchable) AND tons of writings of the saints. Also G.K. Chesterton's Orthodoxy. Less organized but the information is there.
EWTN's Library - I usually end up here after doing a web search but for the first time I actually browsed around. It is not as well organized as I would like but it may have just about any and everything you might be looking for. Lots of council documents, tons of JPII, encyclicals and works by a variety of folks on a variety of topics. In fact, I think I have just found all of those missing ECF references I have been looking for.

Unfortunately many of the documents are zipped so that may be why they do not come up on search engines (or least they used to not) ... Pretty awesome.
Anyway ... I am just curious where folks here head when they are looking for answers about something Catholic.