Yellow Brock doesn't have a single Rock move, and Butterfree pretty much wipes the floor with him. Mankey works too.
In DPPt, the Raichu-Gyarados double battle on Route 210 is pretty damn hard. Raichu paralyzes you and Gyarados cleans up your now much slower team. Not to mention they do a nice job at covering each other's weaknesses on their own...