Three Nintendo-published titles come to mind with poor framerates, all Mario games.
Mario Kart Wii runs at 30fps in multiplayer. The graphics in that game are mediocre at best, so this is pathetic.
Mario Party 8 runs at 30fps on the boards, though fortunately the minigames are 60fps. Once again the game doesn't push the Wii, and also the GameCube Mario Party games run at 60fps.
Mario Strikers Charged has noticeable slowdown when the action picks up. The graphics in this game are more technically proficient than those other two games, but even so, it doesn't seem like anything that should cause slowdown.
I'm sure there are others as well, though these ones came to mind because the lower framerate impacted the gameplay. The Wii is supposed to put gameplay over graphics, so I feel that no game should sacrifice the framerate for pretty visuals or anything else. That's just me though, framerate dips don't bother everyone.