9gag.com

Major time killer and funny to boot.

Apart from forums, I frequent the following:
Wikipedia
Youtube
A whole slew of news sites
Battletech's homepage
facebook

Gaming
Gamespot forums
GOG forums
RPS
Rampant Coyote's Blog
RPGWatch
Game Banshee
Guild Wars 2 Guru
Codex forums (lurk for laughs)

News
CNN
Techdirt

Other Hobbies/Activities
MTGS (EDH/Commander forum in particular)
Gatherer
Youtube
Netflix

Usual Social Networking Crap
Facebook

Facebook
Theregister.co.uk
Slashdot.org
News.com.au
GOG.com

Sometimes go back to
adafruit.com
sparkfun.com

for their blogs.

Gamefaqs, Steam, GOG, various news sites, and several bushcraft and survival websites - because I go outside sometimes :D

Forums:
gog.com - I suppose you already know this site
otcontinued.com - Basically a "talk about anything you want" forum - kind of like this one I suppose, except it's not tied to any particular service anymore
MMO-Champion.com (Off-topic section only, I don't use the WoW part of the forums)

games:
Kongregate.com - I just love playing these flash games for some reason. There's a lot of good ones
steam.com - Just to check if there's anything good on sale. I usually don't buy anything there unless it's at least 75% off.
I occasionally check the League of Legends website patch notes and other announcements, even if I rarely play these days.

Other sites I frequent:
Facebook
Twitter

4chan.org
Rockpapershotgun.com
botherer.org/blog/
idontcareaboutsleep.blogspot.com
raspberrypi.org
forums.eveonline.com/default.aspx?g=forum
eve.battleclinic.com/
journal.davidbyrne.com/
gutenberg.org
omegle.com/
formspring.me

I'm surprised someone finally admitted they visited 4chan.

I guess for me, and in no particular order:

Newgrounds.com(great flash games and videos come out on occasion.)

Youtube.com(for the various music videos I have bookmarked, as well as various scientific videos like Carl Sagan & funny stuff)

Gog.com(of course)

Encyclopediadramatica.ch(The old one is full of suck and fail right now.)

4chan.org(I love the /v/, /co/, /g/, /sci/, /b/, /x/, /vp/, and /gif/ boards myself.)

Various torrents sites(Won't list so as not to be yelled at for linking to em and all.)

Ditto rom sites for older console games

4chanarchive for when 4chan is crap

RPG Codex

The CRPG Addict

RPG Watch (lurking)

Mobygames

I think you just love playing games ;)

Thanks for the feedback everyone, I've been checking a lot of this stuff out.

For gaming - just GOG

For my 3D Art hobby:
www.daz3d.com
www.team-dystopia.com

One other forum but only for a closed group of friends.

Non-forum, just for laughs:

www.collectedcurios.com (many comics - Sequential Art is a great story-driven laugh and How to Play is about gaming)
http://foolsisland.com/silentwinter/index.html for awesome Trollum comics (ok, I cheat, that's my site)

YouTube,Brass Goggles(steampunk forum),Facebook,Newgrounds,GOG,4chan,Domo nation,Know your meme,TGWTG,Spoony experiment.