This list is really out of date, I am working on cleaning it up but many things are broken. I am leaving some broken things up for now while I search for alternate links.

Official Sites

Bioware's Official Mass Effect Site
Official Mass Effect Twitter

ME2 Patches
Your DLC / Entitlements page
Buy DLC for PC

Download Bring Down the Sky (which is free!)
Buy/Download Pinnacle Station

Other Fan Sites

Mass Effect 2 Wiki

Mass Effect Livejournal Community (possible some links contained within could be considered NSFW but they do a good job of warning you beforehand)

Mass Affinity, a program that helps with the long load times bug sometimes experienced with duo-core processors. (2019 note -- this is probably not needed anymore unless you're on what would be considered an old machine in 2010. But the link still works!)

Fuck Yeah, Bioware! - A Bioware-focused tumblr, which I run.

Helpful Game Info

Spoiler-Free walkthrough of how to help ensure everyone survives at the end

A downloadable chart explaining how to save (or kill!) your teammates in the endgame

Video

A helpful video on tweaking the game for a better visual experience.

SSV Normandy Destruction - Battlestar Galactica Style

Zero Punctuation Review of Mass Effect 2

Commander Shepard is still such a jerk. (Mass Effect 1 Version)
Also check out Biggest Bitch in the Galaxy

Fan Trailer - Female Shepard (Very awesome!)

Female Remake of the official launch trailer

Mass Effect 2 CSI Style 1 2 3 4

Legion and Thane on Purgatory

Can someone please help this guy figure out how to beat the end boss? (Yeah I don't know wtf either. :) )

Fan Art Note: These are just pieces I have seen and thought were well done. All should be SFW.

An Unknown Enemy
Thane Krios
The quarian they call Kal
The Funeral
Legion
Skyllian Five Poker
Kaidan

Reviews & Interesting Articles

D&D Tips from Mass Effect 2

Useful Information About ME2

Total resources needed to research/buy all useful projects in Mass Effect 2: (Note that this hasn't been updated since game release so it's a bit more now with new DLCs)
195,000 Palladium
225,000 Platinum (+50,000 for Med-bay Upgrade)
220,000 Iridium
31,000 Element Zero (+5,000 for Bonus Power Training and +2,500 to retrain Shepard's powers)
1,250,000 Credits

Q) Why is this game loading SO SLOW on PC?
A) Goon regulargonzalez has advice:
The Unreal engine has a bug with C2D cpus where loads can take 10x longer than normal. If it takes more than a 3-4 seconds to use the elevator in the Normandy and you have a C2D, here's how to fix it:
1. Start ME2
2. Alt tab, bring up Task Manager, find the MassEffect2 process, remove affinity from CPU 0, click OK.
3. Put the tickmark back by CPU 0 (should have them both ticked now), click OK.
4. Alt-tab back to the game, and your loads should be fast again!

Also note: Mass Affinity, which is linked above, will do this for you automatically.