Any scalable OLAP database (web app scale)?
You can download a free edition (the single node edition) of the greenplum database. I haven't tried it myself but I think/guess it is a powerful beast. Read here: http://www.dbms2.com/2009/10/19/greenplum-free-single-node-edition/
Another option is MongoDB, it is fast and free and you can write MapReduce functions with JavaScript to do analytics.
My reputation here is to low to add a hyperlink to mongodb, so you have to google . I can add only one hyper link per post.