As you reflect upon the fall semester and start to think about 2009, Larry Ferlazzo's list of The Best Science & Math Websites - 2008 is as good a starting point as you could ask for. His criteria is simple: "they have to be free, engaging, and accessible to English Language Learners".
If there's one lesson as important as anything I've ever shared, it's this: anything that works for ELLs will work for all of your students (sometimes better than anything else you might have come up with). So give these resources a good look as you put together your spring semester.