A quick and dirty explanation before we get started. CuuSoo is an official outlet of LEGO, set up like Kickstarter. Only instead of money, you just vote which is way easier on your wallet.
Anyone can submit an idea. If your project receives at least 10,000 votes LEGO will review it (they do this four times a year) and if they can get through all the legal red tape to the final product, the submitter gets 1% of the total net sales.
Still confused? Let this video help:
1. Doctor Who

Despite Nabii's best attempts, the LEGO TARDIS isn't bigger on the inside but it's still a stellar project. Each set would come with a period accurate Doctor, companion and TARDIS with optional daleks and maybe even some weeping angels.
Read more about it and vote it up here.
2. Sand Crawler

MB_Brics submitted this design after weeks of trial and error getting the angles shaped properly. It's made up of over 10,000 individual blocks, including LEGO LED lights and motor. Yep, this beast actually moves.
Read more about it and vote here.
3.

As pointed out by submitter Brickthing, Portal is perfectly set up for modular LEGO sets. This project has pretty specific ideas about how many pieces should come in a set but after that, it's up to you to make the GLaDos test chambers of your dreams.
Read more about it and vote it up here.
4. LEGO Memes

The Internet is leaking again. Dodokiller wants to turn popular memes into desk decoration. Delcare your allegiance for Troll Face, Me Gusta, or Nyan Cat.
Read more about it and vote it up here.
5. Ghostbusters

Well if the new Ghostbusters movie isn't happening, the least the universe can do is give us enough LEGO to make our own stop-motion version. And thanks to TeeKay we are one step closer to that reality. Sets would include Ghostbusters HQ, the library, and the rooftop of Dana's apartment building.
Read more about it and vote it up here.
6. Ninja Temple

This temple is part of a Medieval Japan architecture set thought up by Taxon55. The set would also include a shrine and samurai ancestral home.
Read more about it and vote it up here.
7. Settlers Of Catan

Why play Settlers of Catan on boring old cardboard when Michael's idea would let you build your own board? The entire premise of the game remains the same but in whimsical LEGO packaging.
Read more about it and vote it up here.
8. Lunar Landing

Kids might hate learning but they love LEGO. So let's trick them into absorbing some history with Suzuki's rendition of the Apollo 11 moon landing.
Read more about it and vote it up here.
9. Haunted Mansion

Creator BadSneaker points out this haunted house could easily be modded to become Wayne Manor or even the home of the Munsters. The inside is hollow and the second floor comes off in one piece to make it into a spooky dollhouse.
Read more about it and vote it up here.
10. Avatar: The Last Airbender

Sadly this is just an Appa minifig created by Okay and not an entire Avatar series but baby steps, right?
Read more about it and vote it up here.
11. Glow-In-The-Dark Disney Castles

lg2012 is exceptionally serious about this Disney Castle project. All three prototypes, one for each iconic theme park castle, were approve by Disney to be official merchandise if the project is picked up by LEGO. Each castle comes with different characters and all three are glow-in-the-dark.
Read more about it and vote it up here.
12. Scooby-Doo

The gang's all here. Of course, the dog would be replaced with an official Scooby minifig and the "monster" would just be a guy in a costume.
Read more about it and vote it up here.