I've noticed that Android Market sometimes allow me to download 3d games even when they are not compatible with my device (LG Optimus One p500), for example because the games require a Tegra GPU. Is there a way to filter Tegra-only games from the Market?
Not with the original Android Market, as there is currently no option that would allow an developer to specify the App as Tegra (required|optional) in the app's manifest. Maybe some alternative markets provide this search filter. But I am not aware of one that does it.
Off-Topic: If you want to know which Apps (mostly games) are compatible with your Tegra device, check out NVIDIA Tegra Zone.