I just finished reading The Situation today - it's a terrific example of VanderMeer's wonderfully strange writing. I also highly recommend The City of Saints and Madmen and Veniss Underground, both of which are available through BooksOnBoard (although Veniss Underground can be found cheaper at Diesel-books). VanderMeer has some excellent short stories fiction available online at infinity plus
http://www.infinityplus.co.uk/stories/index.htm (a great source for online speculative fiction generally).
He also frequently puts excerpts and fiction on-line at his website/blog:
http://www.jeffvandermeer.com/tags/read/fiction/