Free-flight or radio controlled?
For free flight, nothings quicker and easier for entry than the Edmonds line, available from a number of online distributors. There are also classics through Semroc such as the Swift and the Hawk, as well as the Nighthawk. Also, for sheer cool and amusement factor, consider the tiny little Fliskits Nanite, which flies on Micromax motors.
For radio control, there's a starter model from Edmonds called the Arcie II, which runs about $40 for the glider kit, or $150 or so for the full starter kit that includes all the gear, battery etc. to fly. You'll be flying in only about 1-2 hours.
If you're into something more challenging, I am a big fan of radio controlled rocket gliders, which are basically just planes with rocket motors. Typically rockets and gliders have conflicting CP/CG requirements, so you have to shift some mass around, change a flying surface, or use a pod that falls off. RCRG's have none of that, but require some care in trimming just right for boost, then adding a couple clicks of trim change to transition into the glide. A great nearly ready-to-fly candidate for this is the Art Hobby Colibri, about $90. I did a conversion thread on rocketreviews.com on this. Another good one is the Venus by Blue Arrow. Greg Stewart posted a very nice conversion thread on rcgroups.com.
