Gossip Girl - The CW
The first season is still one of the best freshman seasons of any drama series to date. It's a shame the writing didn't keep up the pace in later seasons. But Gossip Girl will always be remembered as the series that changed the fortunes of The CW, which was struggling to zero in on a focus as a relatively new network.
The OC - FOX
The OC was a huge hit for FOX when it premiered, thanks to the stellar writing and acting. Unpopular opinion: The final season -- sans Mischa Barton -- was the best one. Don't @ us!
Beverly Hills, 90210 - FOX
Beverly Hills, 90210 is widely considered as the best teen drama ever. It covered some serious themes and lasted a decade. It also spawned a sequel series and a weird reboot.
One Tree Hill - The WB/ The CW
One Tree Hill was never a heavy hitter in the ratings, but every single time there was a threat of cancellation, the fans made their voices heard. It's because the series was actually good!
Veronica Mars - UPN/The CW
This teen drama had something for viewers of all ages. It had a witty teenager who sleuthed her way through high school, a genuinely creepy murder mystery, and a whole lot of humor. The CW canceled it after its third season. But fans raised money to fund a big-screen movie, and Hulu later revived it as a full-fledged series.
Skins UK - E4
The original iteration of Skins is still the best. Every two seasons, the cast was refreshed to keep storylines exciting. It worked!