We really liked Quartz by Elements Interactive when we reviewed it - we rated it "Highly Recommended."
While that's not available for free, Elements Interactive has just released a free holiday follow-up, Quartz X-mas, available here. This is becoming a bit of a tradition - last year they released a holiday themed Li-Nuggz. (Still available.)
If you don't want those (or have them already!) - Nokia also has released it's traditional Christmas game. Pity about the adverts.
