Is there any way to filter out Tegra-only games? 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.