OpenGL practice applications (c/c++)

The last week i learned the basics of using OpenGL.
I played with it a bit and ended up with a decent fake of SuperHexagon (for the time i spend on it at least). 
Now i need some ideas of projects i could make just to improve my skills.
It shouldn't be a large-scale project, as i wont publish nor finish it, just for practice.
A major question i ask myself is, if i should go 3D just yet.

 

From 1 OpenGL Developer to another, http://www.arcsynthesis.org/gltut/index.html is going to be a good place to learn if you haven't already found out about it.

Also, http://www.opengl-tutorial.org/ is another good place to learn. 

3D is deffinately harder than 2D. A good small project is a simple game, its a bit daunting at first having to write a Camera Class, Face Class and dealing with the VBO and VAOs. It can take you a week, or just 2 hours. There are plenty of tutorials you can literally just google for. 

Also, I'd take to learning GLSL (OpenGL Shading Language), writing shaders. Its not extremely hard to implement into any existing application without them but very much necessary. 

PS: Learning OpenGL 3+ is harder when you haven't mastered GL11 (1.1) - GL20 (2.0).