wget -k -K  -E -r -l 10 -p -N -F --restrict-file-names=windows -nH http://website.com/

...and the options explained:

-k : convert links to relative
-K : keep an original versions of files without the conversions made by wget
-E : rename html files to .html (if they don't already have an htm(l) extension)
-r : recursive... of course we want to make a recursive copy
-l 10 : the maximum level of recursion. if you have a really big website you may need to put a higher number, but 10 levels should be enough.
-p : download all necessary files for each page (css, js, images)
-N : Turn on time-stamping.
-F : When input is read from a file, force it to be treated as an HTML file.
-nH : By default, wget put files in a directory named after the site's hostname. This will disabled creating of those hostname directories and put everything in the current directory.
-restrict-file-names=windows : may be useful if you want to copy the files to a Windows PC.

source: http://blog.jphoude.qc.ca/2007/10/16/creating-static-copy-of-a-dynamic-website/