I am pleased to recommend the website Beginning with Moses as an excellent resource for Biblical Theology. There are a number of helpful articles, sermons, and yes, a blog. There are some heavy hitters who are involved with this site (e.g. Graeme Goldsworthy, Simon Gathercole), and the folks who have put it together are doing some fine thinking and writing. I look forward to further exploring the site myself in the coming weeks, but from what I have already seen this site should be bookmarked and visited regularly.