I don't mind the noob tubes that badly, I just take sprinting classes and take the longest paths with lots of cover. Knifing classes counter noob tubes, shotguns counter knives, rifles counter shotguns, noobtubes counter rifles. I have one of each class at all times, cuz they all work.
The cheapest thing I've ever faced is from Shadowrun of all games. It was the smart-link/gust/smg combo. Smart-link gave you lock on bullets, gust knocked you back and killed your accuracy, and the smg killed everyone but Trolls. You could counter smart-link with a different spell, but not gust. Only unblockable spell in the game.
OH! How could I forget? Kill streaks on MW2. Not a terrible problem on Team Deathmatch, but on objective games like CTF or Headquaters, you could camp a corner for 10 minutes, get your harrier/chopper gunner/ nuke combo going, and win with 0 actual points. Match could be (and frequently was) 20-0 in CTF, 5 seconds left, and a nuke is called. TOTAL BS.