There are a lot of free ones online, such as funny games - most of these are quite simple, but if you type 'free online ski games' in a search engine you can find a good number of choices. For example, round games has got more variety and is highly rated by users.

The best ski games I've seen are on a wii, and in general if you want something more special or challenging you may want to think about buying games. You can find a good selection here, with detailed comments from users which will help you make up your mind. Also, if you are thinking about buying a ski game you could look for online reviews of it before you make up your mind.