function gen, as was mentioned, if your into audio stuff, a signal injector/tracer is an easy one to get your feet wet. you can never have too many power supplies, you can build a linear supply from scratch, and get as simple or complicated as you want.
what are you into? if you do some projects that you can use in other areas, it will help you keep focus/intrest. if your into cars, look for things like fuel injector tester/drivers, ect.. im currently working on a simple design for a shot timer. if tis something you get excited about, its much easier to keep interest