Crossovers are always fun. When favorite characters from one show turn up on another, it’s really just added value. I mean, can you think of any series, past or present, that wouldn’t benefit from a walkthrough diagnosis by Dr. Gregory House? No. No you can’t. And, for example, there are some of us who would give up a toe to see Pushing Daisies’ Ned make an appearance on Heroes. 
So here’s a list of Top 10 TV Crossovers. In order to qualify, they have to be official crossovers. Popping up in a dream sequence doesn’t count, subtle allusions indicating that two shows exist in the same world (Sydney Bristow listening to a DriveShaft album) don’t count, and when an episode of one show suddenly turns out to be a video game played by the cast of another show, it doesn’t count. (And I really wanted to include that particular Aqua Teen Hunger Force / Sealab 2021 mash-up.) Characters from one show need to appear on another in character. Richard Belzer’s John Munch-like character on Mad About You wouldn’t count, but any of John Munch’s in-character appearances on everything from The Wire to Arrested Development would.
