Heh, don't know how I went so long without hearing these pointed out!
I know there's a lot in ZUN's stuff, the only one I recognized was a Neon Genesis Evangelion reference (though others have claimed it comes from elsewhere):
To be honest I think it's pretty unfair to call any of these examples plagiarism - a lot of these riffs are fairly accessible and not exclusive to the tracks mentioned.
Ghignarda, please tell me where anybody claimed somebody has plagiarized anything. All I ever did was to say that Kondo got heavily influenced. I never discounted his works.
@RebeccaSugar - Nice video, though the issues he has with self-plagiarism has me kinda dumbfounded. I think the more popular more productive composers have the problem of being typecasted in the styles they are known for, essentially having their previous work being used as temp track in the customer's expectation. Also had to think of Totaka's Song, must be the most self-plagiarized piece ever. ;o)