Star Trek
Star Trek will never leave you. The original series starring William Shatner and Leonard Nimoy ran for just three seasons between 1966-1969, but became a motion picture in 1979 after the success of Star Wars. Six movies were made with the original cast, then they crossed over with Star Trek: The Next Generations in 1994's Star Trek: Generations. The Next Generation cast had three additional films.
Firefly
Joss Whedon's beloved series Firefly only lasted 14 episodes in 2002, but never underestimate a cult hit. Whedon got to continue the space adventures of Mal (Nathan Fillion), River Tam (Summer Glau) and the rest of the crew in a 2005 movie.
The X-Files
The truth was still out there for Mulder (David Duchovny) and Scully (Gillian Anderson). The X-Files duo starred in their first movie while the Fox show was still airing. After it wrapped in 2002 and before it came back to TV in 2016, Mulder and Scully came back to the big screen in 2008's The X-Files: I Want to Believe.
Sex and the City
The adventures of Carrie (Sarah Jessica Parker), Samantha (Kim Cattrall), Charlotte (Kristin Davis) and Miranda (Cynthia Nixon) ran for six seasons on HBO from 1998-2004. The first movie came out in 2008 and a second followed in 2010.
Absolutely Fabulous
Absolutely Fabulous, a British series starring Jennifer Saunders and Joanna Lumley was off and on TV starting in 1992. The show would come and go up until 2012, but party animals Patsy and Edina couldn't be kept down for long. The duo hit the big screen, after years of talk, with the 2016 release of Absolutely Fabulous: The Movie.
Entourage
HBO's Entourage, which starred Kevin Connolly, Adrian Grenier, Kevin Dillon, Jerry Ferrara and Jeremy Piven, aired for eight seasons. The series, which followed Grenier's movie star character Vincent Chase, became a movie in 2015, four years after it wrapped its run on TV.
Veronica Mars
After three seasons on TV, Veronica Mars was canceled in 2007. Talk of continuing the series that starred Kristen Bell as the titular sassy sleuth continued for years before series creator Rob Thomas launched a Kickstarter, stating he'd get to make a movie if fans contributed enough money to meet the funding goal. The goal was met in less than 24 hours and Veronica Mars hit the big screen in 2014. The series will be revived on Hulu as a miniseries in 2019.