What are good (no vendor related) blogs about Business Intelligence and OLAP/MDX ?
Edited: To widen a bit the scope and after the answer of Boyan: blogs/forums related to information visualization and Business Intelligence ?
In addition to the rest of the links in Skarab's comment:
I don't think you will find technical (i.e. MDX/OLAP) blogs which are not vendor-specific. Maybe one site that stands out imho is Kimball's http://www.kimballgroup.com/. The articles and the discussions are often vendor-agnostic and you can get some really good knowledge, too.
Otherwise, for "soft"-er topics, you can read Stephen Few's blog on information visualisation.