Gai Daigoji & Akito Tenkawa, of Martian Successor Nadesico, are both rabid Gekigangar fanboys. The ‘anime-within-the-anime’ idea was pretty nifty.
Sasshi in Abenobashi, Magical Shopping Arcade (both manga and anime). It’s his love of various genres of story that gets him and Arumi transported into various strange versions of the shopping arcade.
Heck, you get brief glimpses of his room in his flashback scene with Mr. Incredible – just look at all the schlock he’s got. Pure fanboy. 
The words you want is simply ‘otaku’.
Otaku no Video (Otaku’s Video) is the title of an early Gainax movie about a group of anime otaku.
And O’Niell’s a Trekkie.
Examples:
‘Inertial dampeners?’ ‘… Cool. … And check. Phasers?’ ‘Sorry, Sir.’
And his insistance that the Prometheus should be named the Enterprise.
Koppy McFad aka Supersnipe was probably the first fanboy superhero (at least, the first who was a comic book fanboy). According to the blurb, “He reads 'em, he breathes 'em, he sleeps 'em – the boy with the most comics in America.” This was in 1942.
Ralphie was a huge fan of Little Orphan Annie.
Mulder’s seen Plan 9 From Outer Space 42 times.
Well, Peter Griffin of “Family Guy” is a KISS fanboy!
Frank Mellish in the comic strip Liberty Meadows is definitely a fanboy.
He’s a fanboy of all sorts of things! He wanted to name Meg “Twikie”, but Lois didn’t think kids would get the reference.
Bideebideebidee
The entire cast of “Welcome to Eltingville.”
Sigh, I would have liked to see where they went with that.
IIRC it was Jeff Albertson.
Remington Steele was an extreme film geek. One gets the feeling that his entire training regimen for the detective biz consisted of watching old movies over and over.
Krokodil, so true.
The anime TV series Martian Successor Nadesico starts off with one character being a fanboy of another fictional anime. By the end of the series the whole cast is following this show. :wally
I don’t get that reference.
Btw, let’s also remember that Peter’s TotemAnimal/SpiritGuide in his vision quest was Fonzie.
Twikie was the egregious robot from the also-egregious Buck Rogers 70s TV show.
Oh, and to contribute something on-topic, Randy from Scream was a horror movie fanboy, and so were the killers, Billy and Stuart.
Bart and most of the child characters on The Simpsons could also probably be considered Itchy and Scratchy fanboys (as opposed to Krusty proper).
Data from Star Trek: The Next Generation seems to be a Sherlock Holmes fanboy.
There are several characters in Galaxy Quest who are rabid fans of that fictional show.
In the PBS cartoon show Arthur, Arthur and most of his friends are fans of the Bionic Bunny.
I figure stuff like Welcome to Eltingville, or Downtown might be too easy (since the premise is geeky characters).
On the other hand, that brings up Undergrads, which has Gimpy, the Uber Star Wars fan, and ‘Number One’, the Star Trek geek who he clashes with occasionally.
The kids of South Park love Terrence & Phillip, even going so far as to watch “Russell Crowe’s Fightin’ Around the World” just to see the latest T&P movie trailer. 