There aren't that many TV shows out there that are specifically about time travel. There may be the odd episode but... time travel, I find is more a of movie game. I did want to use Outlander again but I thought I'd challenge myself. Saying that, I think I've used all three picks before...
Don't forget to check out where it all started over at Wandering Through the Shelves.
I much prefer the genius of Futurama than the never ending Simpsons. I know they came first and weren't cancelled multiple times but Futurama has continous wit and personality as well as bizarre surprises and the fact its set in the future, literally anything can happen to the Planet Express team. For those not familiar with this slice of awesome-ness, it all begins on New Year's Eve in 1999 when 25 year old Pizza delivery guy Philip J. Fry ends up frozen in a cryogenic pod that opens in 2999. He has best friend, Bender, a foul mouthed alcoholic fueled bending unit robot and a friend/co-worker/later girlfriend Leela, a one eyed alien pilot (later to be discovered, a mutant). Together they are part of the Planet Express delivery crew along with other weird and wonderful characters. There are specific episodes where time travel is used, such as the episode where Fry and the crew travel back to the 40s on Earth and Fry becomes his own grandfather. With 8 glorious seasons and some comics to boot, it seems like this great show has been put on the 'what a great time that was' shelf.
Ashes to Ashes