I think there are a variety of ways to use a blog in science classes. Safety issue discussions and information, ethical issues in science, scientific breakthroughs in the news, etc. These could all be graded as daily grades based on comments to posts.Depending on what type of science you teach, students could work together to make a blog project for class. For instance, if you teach chemistry, have students break into groups and do blogs about different kinds of bonding structures and the implications of those. Or even about different groups of elements. Let the kids research and then post - using pictures, links, videos, etc in their postings. The students in the other groups could go to their blogs and read and comment. Similar things could be done in biology and physics.You can have more than one writer in a blog - so a group of kids can easily work together. This would also be a way to share about some famous scientists of the past. Both the blog posts and the comments can be graded.
Bookmarking is a great tools for keeping the required information on your tips. I am on the online community of AP Teachers for Biology. It is a wonderful place for sharing our thoughts and asking for help when needed.
Tool 3You Tube has some wonderful videos which help the students in understanding the complicated concepts easily like Protein Synthesis and Fertilization in Flowers.I download and use many videos in the class.