I don't really need another place to blog, but the Writing Initiative that I direct at Passaic County Community College has an Initiative blog that we use to communicate with our campus community. Though some of the posts are directed directly at our students and faculty, a number of the resources we write about are useful to anyone doing writing across the curriculum.
For prewriting, mind maps on paper, and now electronically, are popular idea-processing tools. Their use was popularized by the British IQ specialist Tony Buzan starting in the 1960s.
Bubbl.us, CoSketch.com and Cacoo are good starting places that also allow collaboration by student pairs or groups. Of course, students can also use The Times for generating ideas on many topics across disciplines from math to fine arts.