Recommend me some good Youtube series.

jklproductions, blendtec, fridaynightcranks and siggas

TableTop. MediocreFilms' Douchebaggery. DailyGrace.

goom garps

Mmmmhhh ERB! - Season 1 and Season 2

ERB stands for Epic Rap Battles of History, a prime example of how Epic these are are something like Beethoven vs Justin Bieber, or Bill Gates vs Steve Jobs, great material, funny as hell.

Annoying Orange?

Angry Joe Show. He makes awesome game reviews.

goomgramosgrumblerumos GAMEGRUMPS

you may or may not like it, the shows called metadating, you can watch it on the geekandsundry channel

Red vs Blue!

These channels should keep you occupied for a few hours:

Cyanide & Happiness

College Humor

WKUK

Between Two Ferns w/ Zach Galifianankis

Game Grumps

Two Best Friends Play

Angry Joe Show

Jesse Cox

Two best friends play

Team Four Star

If you like Sci-fi, you might enjoy the H+ web series

If you're into minecraft (or even if you aren't!) check out all the guys on the Mindcrack server. There a subreddit for it at r/mindrack. It's a minecraft server with a collection of really good LPers that all have great personalities. I spend hours a day watching their videos.

Game Grumps
Screwattack Channel (Hard News, Death Battle and other interesting shows + video games related stuff)
DMJared
PeanutButterGamer
Nathan Barnatt (right now he's making Beat Tom, it's pretty interesting)

There are many good animators on YT, I recommend subscribing to:
OneyNG - Leo & Satan
PsychicPebbles - HellBenders (with Oney)
RicePirate
TerminalMontage
Cartoon Hangover - Mainly for Breavest Warriors - from creator of Adventure Time
RedMinus
Ukinojoe
and obviously Egoraptor, though he didn't upload new things for a while now. But he's close to finishing PokeAwesome 2 and Zelda Sequelitis, I hope.

Not really series, but if you're asking for general channels that are awesome I'd recommend LaBlogotheque (music) and theRSAorg (academic)

Space Janitors is really good :)

Go watch H+, it's really great!

Marble Hornets!

The online gamer is funny as fuck

community channel!!!!

Arby 'n The Chief
NEW SEASON SUCKS START WITH THE OLD.

This is hilarious: http://www.youtube.com/user/Tobuscus/videos?query=literal

All of my faves have been mentioned... except Dick Figures!! This is one of the raunchiest web series I've ever witnessed, with TONS of randomness spread thoughout 5 minutes of pure awesome. Even better, a movie is in the works, so now's the best time to watch!

If gaming's more your thing, Zero Punctuation offers rapid-fire video game reviews with some hilarious commentary and neat illustrations. It's not for the faint of heart, especially when you see him rip into one of your favorite games (which he will do), but it's still a hysterical review series nonetheless.