It can be anything.
80s / 90s, Anime, CGI etc.
Who knows? Someone may post a link to one show that you long forgot.. Nothing can beat feeling all those memories rushing back to you.

Some of my favourites -
Batman the Animated Series [ 1992 ] - http://www.youtube.com/watch?v=A71i0a5x-qA [ Animation at it's best. This is THE Cartoon. ]
The Real Adventures Of Johnny Quest [ 1996 ] - http://www.youtube.com/watch?v=dGFUijdwWdk [ Seriously, Can anything get more Epic than this? CGI in a Cartoon in 1996! ]
Dragonball Z [ 1997 ] - http://www.youtube.com/watch?v=S9kN0pct-Q8 [ One of the best Anime Intros ever ]
Swat Katz [ 1993 ] - http://www.youtube.com/watch?v=K_AdxJWFUh4 [ Rock on. Rock on.. ]
Superman the Animated Series [ 1996 ] - http://www.youtube.com/watch?v=oUcKJflBG8Q [ Another Great Warner Bros. Classic. ]
Spiderman the Animated Series [ 1994 ] - http://www.youtube.com/watch?v=YEoPQ1-GC7I [ Much better than that Immature Ultimate Spider-Man lol. Just my opinion. ]
Alvin and the Chipmunks [ 1983 ] - http://www.youtube.com/watch?v=DFxgFvbPGSg [ Lol, I just had to include this.

Batman Beyond [ 1999 ] - http://www.youtube.com/watch?v=Nx23F5mjlC0 [ Really shows that 90s Rave Style. Great Cartoon too. ]
13 Ghosts Of Scooby Doo [ 1985 ] - http://www.youtube.com/watch?v=iWCsW3UTYUQ [ Great Scooby Series. This one was really creepy when I was a child. ]
Tim and the Omegas [ 2012 ] - http://fav.me/d5522zu [ Just kidding lol. Intro seen at the start before the Soundtrack and Picture. Was really a test. ]