These 2 get my votes. I definitely like the crystal one too. I think the second is very simple but if done right could look really good. I really don't think I'll be able to take part in the following month for a number of reasons, but I'd really love to do that crystal scene. Could always hold out a month on it :D
I also don't really get the temple, it's the same as the last one, just another setting. just adding another suggestion: (altough people that have done a couple of challenges might be tired of the sci-fi'ish stuff by now) Maybe it might look a bit much at first, but if you analyze it I don't really think it would be that…