SWTOR Resources (Mostly) Up to Date
Most up to date sites:
Merlyn's SWTOR Guides
The most thorough class guides I've found that are updated pretty regularly. Includes everything you need to know about playing every class at the end game with an overview that gives you an idea of how the class plays, it's role in raids/parties, and where it stands relative to other classes.
ExRD
My favorite SWTOR YouTuber. Not a multiboxer, but they regularly post solo MasterMode (aka Heroic) runs. Since they're running solo, there's a lot of good info to be gleaned from how to most efficiently run heroic dungeons, and which classes are probably the most powerful to pair. It's also just damn impressive. There are some other games here too, but SWTOR is the one they come back to the most.
Vulkk
A pretty good site that covers the basics of the game, as well has some class guides. The guides are written by various players, so the quality changes from guide to guide. The guides are also not necessarily updated very often.
Swtorista
Tons of guides here covering every aspect of the game, including cash shop cosmetics/items. Lots of good info, updated regularly. They also have a YouTube channel. The channel has a lot of great videos for new players, as well as up to date news.
Parsley (You may get a warning from your web browser about this site due to an invalid certificate)
Okay DPS parse info. SWTOR does not have the huge fanbase that WoW does, so its info base is lacking overall. StarParse is another site that has data, but I have no idea when that data was last updated. Parsely tends to update after every major patch. On the upside, SWTOR DPS classes are all very close to each other on the top end, so the data isn't necessarily that important.
Less up to date sites:
StarParse
Another parsing site. Includes tank and healer data as well, though how up to date it is I can't say.
TorCommunity
Pretty out of date when it comes to class guides as they're still on patch 5.X, when the game just patched to 6.1 today (2/17/21). It has other information too though so it could be helpful.
Dulfy
Used to be an excellent source for class guides, then went dormant some time ago. Recently seems to have been updated with one new class guide, a change to the overall layout that broke a lot of old links, and made it harder to navigate the site. Mostly linking for posterity.
There may be a few other decent sites out there, but my needs are met with the ones I listed first. Let me know if anyone has any other good ones to add to the list.