Good seeds for me are areas with a nice area of flat land, and I enjoy super-big snow biomes too, as one of my first maps from Beta 1.4 (when I started getting really good at Minecraft) was a snow biome, and I'll admit, I was amazed. The "perfect" seed has got a nice flat land, enough space to make a house and some farms, as well as a forest that is nearby, and some cave systems too. I know I sound finicky, but I've found a lot of maps like that.