I don't know if it's the kind of thing you want to add, but there are a lot of trading resources, too:
backpack.tf - community-voted pricing (so it's more fair) for all TF2 items; prices listed here are generally considered the "standard" value
backpack.tf: unusual version - same, but for your shiny unusuals
tf2outpost - post to buy/sell your pixels (recommend checking backpack.tf first, so you know what a fair price is! Also, be very careful with anyone adding you if you post a sale—there are a fair amount of scammers with phishing links.)
scrap.tf - automated bots buy your keys/metal/hats/weapons in return for metal/keys (more for low-ticket items like regular ol' hats, or converting any 2 weapons into scrap when they're not for the same class)
I'd personally include the league pages, too! Maybe someone came here because they saw TFTV featured on Twitch or something. It can't hurt, right?
UGC - free to play competitive leagues for Highlander, 6v6, and 4v4; many skill divisions so a good place to start your comp career!
CEVO - paid 6v6 league with two skill divisions, growing
ESEA - paid 6v6 league, high skill ceiling
There are also the irc channels for pugging, which not everyone seems to know about. You can connect with an irc program, or use ATF2 in your browser. They're generally higher skill than the lobby sites and require mumble (which they provide) during games.
#tf2mix - friendly to newer 6v6 players (but most people have played a fair amount still) because it alternates Captain/automatic picking; if you aren't picked the first game, you're automatically put into the second
#tf2.pug.na - high skill 6v6 pugs, all games are Captain picks so it may take some time to get in, often starts late at night
#tf2.mix.nahl/#tf2.pug.nahl - Highlander versions
Tip: meds are usually the hold-up. If you're pretty comfortable with the medicine man, queue up to get some games started. As people get to know you for being decent/nice, you'll get picked for other classes, too.
#tf2scrim - find scrims for your team, usually ESEA/CEVO teams looking for that week's map. State your skill level, what map you're looking for (or that you'll play any), and y/our server (if you have one, need to play on theirs, or don't care either way)
Finally, after doing all those lobbies, mixes, configs, and jumping, you want to play on a team but aren't sure how to find one? Make a post with your experience, the classes you play, and when you're available to scrim/play games.
UGC recruitment - for UGC Highlander, 6v6, and 4v4 across all divisions. If you're just starting out, try here first!
TFTV recruitment - if you've played a few seasons and are looking for a CEVO or ESEA team, you'll have more luck here.
That's it off the top of my head, this is a great idea and I hope it helps people. :]