You'll probably want to embark on the wonderfully frustrating world of lighting. The Arcsynth tutorials are really good at explaining the per vertex lighting. However, you'll want to move into per-fragment lighting soon after that (also called Normal Mapping).
After that, it really starts to come down to what you want to do with the graphics. You may need to get into particle emitters or Frame Buffer rendering and so on.
But it's important to the proper ground work in first. I suspect you may be using the fixed pipeline functionality, it seems to be a natural direction everyone gravitates to when starting. I strongly recommend you ditch that and use OpenGL 3.3 or higher. Here's What I Iecommend:
1.) Use Arcsynth to get a solid ground work. Make sure you're using things like Vertex Array Objects, Vertex Buffer Objects and non deprecated functionality. As I mentioned, it's also a good source for per vertex lighting. It does have some useful information on textures as well.
Is a great resource for beginning to intermediate tutorials. I think they have the absolute best explanations overall. I recommend learning things like normal mapping and Frame Buffer Objects from here.
This also has some beginner and intermediate tutorials explaining things like normal mapping and so on. In the beginning, it'll just be a nice place to ping-pong between if another tutorial isn't making sense. Much later on down the road, it becomes a great resource for more advanced concepts.