And remember, because of rampant crossover fever, more than 100 past and present series are all figments of young Tommy Westphal’s imagination. Basically, your favorite show was created by an autistic child staring into a snow globe.
10. Diff’rent Strokes / Silver Spoons – Possibly my first crossover experience, and it blew my young mind. Arnold Jackson shows up to interview Ricky Stratton for the school paper, and accidentally 
publishes the blueprints for an experimental military aircraft. Why would a student reporter interview a kid from another school? Since when were the Strattons taking military contracts? It didn’t make sense, now that I think about it. On the plus side, Myndi doesn’t even remember this and if you can beat her to an 80’s reference, you need to freeze that moment in amber.
9. Mad About You / The Dick Van Dyke Show – If you remember the 90’s, you remember that NBC mandated numerous sitcom crossovers. So now there are all these awkward scenes in syndicated episodes of Friends where they expect us to remember that Caroline in the City was, apparently, a real thing. That was an irritating time in our history. But here, there’s very little commercial consideration since Mad About You crossed over with a series that ended 30 years before. In this episode, Paul Buchman gets a chance to work with the legendary Alan Brady (Carl Reiner reprising his role). Carl Reiner? Always funny.
8. The Fresh Prince of Bel-Air / The Jeffersons – George and Weezie actually made two appearances on Will Smith’s sitcom. Will and his fiancée met them in marriage counseling, and near the end of the series, the couple tried to buy Uncle Phil’s house. Actually, Arnold and Mr. Drummond put in an offer, too. Isn’t it nice to know that they stayed together all those years?
7. Cheers / St. Elsewhere – Some of the doctors from Boston’s St. Elgius stopped off for a drink at our favorite bar, where they were served by Carla and hassled by Norm and Cliff. Now, I remember this meeting happening on Cheers, but the Internet assures me that it was actually on St. Elsewhere. Unfortunately, I can’t confirm this definitively or come up with any more details. You know what’s not available on DVD? St. Elsewhere. You know what really needs to be available on DVD? St. Elsewhere.
6. The Venture Bros. / Jonny Quest – This one is pretty fantastic. An episode of Venture had the cast looking for the scattered pieces of one of Jonas Sr.’s inventions. One component was stashed in a tiny 
underwater lab, where the now-adult and heroin-addicted Jonny Quest had spent the last couple of decades. What’s notable is that the character is actually called “Jonny Quest” (and a previous episode featured the death of a clearly-identified Race Bannon), and since Cartoon Network is owned by AOL/Time-Warner, a company which controls the rights to the Hanna-Barbera stable, that makes this an official, sanctioned crossover.
5. The Simpsons / The X-Files – When Homer spots a glowing extraterrestrial in the woods, Agents 
Fox Mulder and Dana Scully come to Springfield to investigate the case. What’s notable is that Mulder and Scully are mostly played straight, and just dropped into the weirdness of the Simpsons universe. This episode also features appearances by Marvin Martian, Chewbacca, Gort, and ALF.
4. The X-Files / Homicide – A flashback episode of The X-Files revealed how underground publishers and conspiracy nuts The Lone Gunmen met. The story is reconstructed through statements and interview by the Gunmen, after they’ve been arrested by the Baltimore police and questioned by Homicide’s John Munch. Since Munch is known for his paranoid theories, he fits into the world of X-Files perfectly. The story is well-executed anyway, but the addition of Munch makes it a classic.
3. The Daily Show / The Colbert Report / Late Night with Conan O’Brien – During last year’s Writer’s Strike, the late night hosts were left scrambling to fill airtime. It began with a joke feud between Stephen Colbert and Conan over who deserved credit for Mike Huckabee’s strong showing in the primaries. They sniped at each other on their respective shows (and Colbert showed an early interview in which Conan shot and killed him), until Jon Stewart appeared on Colbert with a clip of his old MTV show and an interview with Conan. Finally, the hosts spent a night appearing on each other’s shows and making plans for their big fight. And then, Late Night presented the fight, a lengthy video segment with slapsticky, goofy stunt work, and sheer absurdity. I loved it.
2. Batman: The Animated Series / Superman – Sure, Batman and Superman have met each other a million or so times by now. But back in the late 90’s, their respective animated series presented a three-parter where the two characters met for the first time in that continuity. With some unexpected twists to the mythology (the Bruce Wayne / Lois Lane romance) and the combined villainy of Lex Luthor and the Joker, this crossover was clever and action-packed. After this, the animated versions would meet many more times, including five seasons of Justice League. When Superman meets Batman, we all win.
1. Homicide / Law and Order – These two shows featured a two-part crossover every season for about four years, but it’s the first one that really stands out. A poison-gas attack in Washington DC bears some similarities to an open case in Baltimore, which means the police from both cities work together to find the perpetrator. It’s really great the way the two casts fit so seamlessly into the same world. (We even learned that one of Munch’s multiple ex-wives rebounded with L&O’s Lenny Briscoe.) And what’s interesting is the way they maintain the feel of the two shows. The 
Washington cops are alarmed by Frank Pembleton’s style of interrogation. Because Law and Order is more of a procedural about how the police and District Attorney use the law to solve and prosecute crimes, while Homicide was more of a character drama that looked at big themes and unanswerable questions. This disparity between series styles translated into a fundamental philosophical difference between the casts of the two shows. It was an interesting approach that left fans of either series satisfied.
There’s my Top 10 list, and believe me, you just missed out on a lengthy entry of Charles Nelson Reilly’s “Jose Chung” character from The X-Files moving over to Millennium. That would have been number 11.
