Sliders, on FOX (s1-3) / Sci-Fi Channel (s4-5)
Originally on FOX, then it was cancelled and had another two seasons produced by Sci FI. I didn't really see it then, I guess. Um, but anyway it was a pretty cool show, for the FOX seasons. This genius college kid named Quinn Mallory created this device to slide between parallel Earths, and he and some other folks- Professor Maximillian Arturo; a friend of Quinn's named Wade Welles; and Rembrandt Brown, who was a sort of Motown singer looking to make a comeback- all got sucked into this other world without setting their home coordinates, so they got lost and kept sliding to different worlds having weird adventures and stuff.
Later in the series, there were these creatures called Kromaggs from a world where they'd evolved alongside humans, and then they developed sliding technology and started conquering all the other Earths. And stuff. Actually a lot of other things happened on this show, and it was cool and fun. And the cast changed somewhat. I'd like to say more, but... there were some plot developments and stuff that would be too spoilerish.