I say there are three ways to "move on". Pick the one that suits you. In order of easiest to hardest:
Steeping grains- Just start soaking a pound of crushed grain in your water. Pull it out when the temp hits 160. This will give your beer the flavor of the grains. The cost will be a buck and a half for a pound of grains and a quarter for each grain bag.
Recipe Formulation- Learn to make the different styles of beer by inventing recipes. Of course, you will still be using DME/LME, but you can play with the hops and the yeast and the steeping... that's enough variables to keep you entertained for a few batches. To do this, I suggest you pick up a brewing program, like BeerSmith for example. Most have a free trial. Also, maybe pick up a book on clone brewing (make sure it's aimed toward the extract brewer though)
Partial Mash- do a search for "Mini MLT". Somebody created an awesome 2 gallon Mash Lauter Tun from a tiny cooler, total cost was under $20, IIRC. You can learn all about how to mash and, really, the basic procedure can be explained in a couple of paragraphs. The concept is complex, but the procedure is simple. In fact, I will tell you the procedure right now. Add 2-3 pounds of crushed grain to a cooler. Add 2 quarts of hot water per pound. Hold the temp at 154 degrees for an hour, drain the water. Repeat with 160 degree water. Drain it. Add your DME/LME to that. It's really pretty much that simple.
Of course you can also partake in the other side-hobbies. Yeast propagation, grow your own hops, malt your own grain, etc.