Inexplicable ping spikes/lag?

[Shodo Uban]

I'm a gamer as well.|
Sometimes it's their side , sometimes it's ours , sometimes it's the ISP...
Anyway , what game is it and where are you on the planet? ( may or may not matter , trying to rule things out )
Tried resetting your router? Letting those puppies do a little reboot here and there can solve a lot of crap like that.
Have you run a trace route on it when it spikes?
( Comcast sucks .. I know you know that but I still just had to say it ... )
Have you tried running Leatrix fix 3.0? google it , don't take my word for it. http://www.leatrix.com/
Does it only happen on that one game , all games , JUST games..\ not on youtube etc ..??