Buying and Selling
Magic Card Market - European P2P buy and sell

Trading
Deckbox - Obviously. Worldwide & practical trading tools

Youtube Channels
MTG Goldfish - Daily new gameplay video's with excellent commentary
Channel Fireball - Pro players playing MTGO and informative interviews
The Magic Show - Weekly 75 minutes show with all things magic
Alpha Investments - Funny guy talking MTG Finance
Strictly Better MTG - Budget Decks, Brews and Spoilers
Desolator Magic - Saltyness with Cascade
Tolarian Community Collage - Excellent product reviews, MTG stories. Simply the best out there!
Pauper Fox - Pauper!
MTG Goldfish Replay - Replay of MTG Goldfish streams
Gathering Magic - All sorts of video's
Unsleeved Media - All sorts of stuff, many product openings
Star City Games - Daily News (Split Second) and many gameplay video's
Windmill Slam - News and game shows
The Mana Source - Popular channel with spoilers, decktechs and more
Seems Good Magic - Daily Drafts
Rogue Deckbuilder - Budget decks, brewing and MTG Finance
GG Degree - All sorts of magic video's
Aether Hub - Deck Tech, Lore and more
The Magic man Sam - Art, Cards, Alters, Lore and Deck Techs
Budget MTG Decks - Budget Decks in all formats
Mythic MTG Tech - Modern, Legacy, Vintage and Commander deck strategy
MTG Strat - All sorts of stuff
Command Zone - Commander!
Heroes v.s. Legends - Spoilers, Set reviews, decklists and more


Decklists & Articles
MTG Goldfish - Prices, Articles, Decklists and daily updated!
TC Decks - Latest Decklists
TappedOut.Net - Community Decks, draft simulator and goldfish playtesting
Hareruya MTG - Decklists and articles
MTG Top 8 - Decklists!
EDH Rec - All EDH Decklists and statistics
MTG Salvation - One of the largest MTG forums
/r/magicTCG - MTG subreddit

Other
Mythic Spoiler - Newest card spoilers!
MTG Cast - ALL MTG Podcasts in one place!
MTG Coverage - Replays of large events coverage (GP, SCG, Pro Tour ect.)
Twitch Magic - Official GP coverage by Wizards
Twitch Magic2 - 2nd Official GP coverage by Wizards (in case two events at the same time)
SCG Live - Official Star City Games event coverage (great commentary)

Art Of MTG - MTG Artwork
Hypergeometric Calculator - Probability Calculator

Play Magic online
xMage - Download and installation instructions for xMage
XmagePlayers Facebook group - relevant info and private server (in case .De and .Us are offline)