dune1980r had the good idea of us giving our personal memories of all the Big 12 schools and I'm bored today so here goes. These are just my best memories of football games, if you all want to add other sports too that's great.
Nebraska: Tons of infuriating, heart-breaking losses over the years but 62-36 is my all-time favorite CU game by far. I don't need to go into detail because every CU fan remembers that game clearly.
Kansas State: My second favorite CU opponent. Lots of memorable games for me. My freshman year at CU they came in ranked 5th and we were ranked 14th. We lost 16-9. It was a pretty good game, but what makes it memorable for me was a bunch of KSU students came over to the student section late in the 4th quarter to talk trash and start a ruckus. Needless to say being outnumbered about 10 thousand to 10 it didn't end well for them. There were two great CU victories with amazing finishes that also really stick out for me. There was 2002 where Donald Strickland absolutely BLEW UP Darren Sproles on the sideline on 4th and goal to seal the victory (and I was literally 20 feet away as I was right on the goal line 5 rows up, best view I've ever had on a big play) and 2004 where Ron Monteilh scored a 64 yard TD with 5 seconds left to win. Tyler Hansen almost single handedly beating them in 2008 was pretty good as well.
Iowa State: Not really an "exciting" opponent but there were some good games over the years. 2002 was my most memorable. It was for the Big 12 north title and we beat the Seneca Wallace led Cyclones 41-27. This and the 62-36 game were the only two times I ever took part in a "charging of the field" after a victory.
Oklahoma: The 1994 CU-OU game was the 2nd CU game I ever attended (after NE Louisiana earlier in the same season). We smoked em 45-7. I also vividly remember watching the 1995 game on TV. That buffoon Schnellenberger was their new coach and I seem to remember him running his mouth before the game. We smoked em again. In Norman. Ahh... the good old days when we were good and OU wasn't. I guess those two games are officially not "Big 12 Memories" but "Big 8 Memories" but oh well... I didn't get to go to the 2007 game but it was a blast to watch on TV. I'm not sure it is really a game that CU fans should look back on fondly though. I would call it the "mirage" game. After the game I thought "wow, that Cody Hawkins kid is gonna be a solid QB" and "it looks like Dan Hawkins has things headed in the right direction." Wrong on both counts, and that game was probably the main reason Dan got his contract extension.
Texas: Had to watch it on TV but the Big 12 championship game victory is obviously one of my favorite CU games ever.
Texas A&M: We had some good victories against A&M but none were all that memorable to me. I certainly remember the 1995 game where Detmer got injured and Hessler came in to lead the Buffs to a win over the #3 ranked Aggies. That was pre-Big 12 as well though... 2000 was memorable because it was Craig Ochs' coming-out-party but then a few short months later he was gone...
Missouri: Mizzou is a weird one for me. It seems when we were good our victories over them were never that "memorable" and lately they have absolutely dominated us. Hopefully someone else will refresh my memory.
Texas Tech: Ahh, the one team Dan Hawkins could beat (well, until last year). The 2007 game was a pretty good one, and of course there is the 2006 game where we charged the field after improving our record to a stellar 1-6 (gag). I'll go back again to my freshman year at CU: In the 1998 game we were both ranked, we got a hard fought victory, and I'm pretty sure it was a night game. Sorry I can't do better than that :-)
Oklahoma State: I remember the 2001 game being a really hard fought victory and I remember the 34-0 smack down we put on them in Stillwater in 2005. The 2009 game still pisses me off just thinking about it...
Kansas and Baylor: I'm gonna give the ultimate insult to these two and say that it was never that big of a deal when we beat them and losing to them was always devastating so there aren't really any "great memories". I guess the 2009 game against KU was pretty good but last years loss was 100 times more "bad" than 2009 was "good".
Writing this I am surprised how few details I remember about seasons prior to the Hawkins-era (other than 2001). Hopefully someone else can do better.