Sharepoint Space Monitor
How can you monitor the disk space usage in your site collection? Just how much space is that subsite taking up?
Up until now the only suggestion might have been to use the _layouts/storman.aspx page. This was unsatisfactory however because it required Site Quotas to be set, and didn't report size by site. If those compromises didn't work for you, then custom coding was your next option.
That's not required anymore! Tim Dobrinski has been coding his cotton socks off again to produce another free tool for the Sharepoint community. His Sharepoint Space Monitor should nail the Sharepoint Site size reporting issue once and for all.
As I say, the tool is free, and can be found via this link; http://www.thesug.org/blogs/lsuslinky/SSM/Pages/default.aspx