As far as brands go, Beeman, RWS/Dynamit Nobel, Air Arms, Theoben, HW/Weihrauch, Webly, and Logun are all top-quality. Beeman is actually an importer/rebrander of various HW, Webly, and Theoben models. They tack on a premium, but you also get a better warranty. In general, avoid Gamo and Chinese brands (Tech Force).
For a starter plinking air rifle, you want to go for a spring piston-powered .177 caliber, as the ammo will be much cheaper and the trajectory will be flatter compared to larger calibers. There is a relatively limited selection at the $200 mark, but if you increase your budget to $250-300, you can pick up a Beeman R7 (HW-30). This is widely touted as the absolute best plinking rifle around, as it balances light weight, an excellent trigger, low cocking effort, excellent accuracy, and low hold sensitivity with all-around solid German construction.
The trend in the past few years among airguns is higher velocity/power. While higher-powered air guns have their place for varmint hunting and pest control, they afford practically no benefit for plinking and target shooting. The R7 is a moderate-powered gun, and will suffice for shooting targets out to ~35 yards with iron sights (if you are sufficiently skilled)- extend that to 40 yards with a good scope. 50 yards is pretty much the upper limit with any airgun, due to constraints of the small, lightweight pellets.
Try straightshooters.com for general information- if you need more info, feel free to shoot me a PM.
