There are many around, I will obviously recommend my own sitemap generator tool which in its newest version can handle a lot! I write a lot because I have not had the patience to test beyond 200k pages But with the metrics I use, I would say, depending on the computer, memory available etc. one million should be possible... However, crawling a million of pages takes time... I will get around to test it some day though Anyways, else check: http://code.google.com/sm_thirdparty.html
I use the http://gsitecrawler.com/ generator. It doesn't have a upper limit, it's free, and works. It's just seems slow. Jim Catanich