GeoGebraTube.org is one of the great things about GeoGebra 4. Easy to store your sketches, distribute to students, access from anywhere, etc. It's searchable like YouTube, and has been an amazing resource for getting teachers started with the program. They can find what is useful to them, rather than feel like they have to be able to make it themselves. But they see enough to help them want to be able to do it for themselves. Here's a short list of recommended sketches from a recent group of beginners. (Here's our current Intro to GeoGebra workshop, which has a Guide to Getting Around GeoGebraTube. If you're in driving distance, I give that workshop for free.)
But one of the things I love about it is that sketches have a link to the author's profile, which is really just a list of all the sketches they have uploaded. So I thought I'd introduce you to my favorite authors. These guys are not doing things for beginners to emulate (in most cases) but do showcase the possibilities of the program. I'd be very interested in knowing your favorite GeoGebra authors. The linked name goes to their GeoGebra profile
Daniel Mentrard - extremely prolific. Has a website, too. (French) Investigates neat problems and seems to push the limits of the program.
Starter sketch: Check out his Polar Coordinates game.
Anthony Or - so creative. Has a YouTube channel and is on twitter. Seems to design for curricular use and has very practical sketches for student use, in English and Chinese.
Starter sketch: one of his neat dissections.
yuri1969 - creates a wide variety of sketches, mostly in Polish. (I think.) But useable for many because math is such a universal language, of course.
Starter sketch: Balance, also his neat 3D models.
Micky Bullock - relatively new to me, with an awesome sense of design. Has a website and is on twitter. Attacks very cool problems.
Starter sketch: ultimate projectiles applet.
The problem with any list like this is that you leave off so many worthy names. I love work by Dan Anderson, Guillermo Bautista, Nicholas Erdich, David Obrador, Dave Radcliffe, and more. I wish benice and Marc Renault shared on the tube - both are amazing. Please leave any suggestions you have for GeoGebra authors in the comments - I probably have just not found them yet! For completeness, I guess I can link my profile. I'm not in these guys' class, but I do take requests!