A perl wrapper to the international spelling engine, iSpell: very handy. Will tell you which words it didn't know, what it thinks they should be, or how it could be formed from a root.
This is not an XS interface, but pipes to ispell, which is not required by the makefile. However, if you don't have it on the path, you will get errors along the lines of 'unable to open ...' This is particularly hard for users restricted to Win32 without a C compiler, since there is no official binary build of iSpell. Such poor individuals may wish to examine Text::Aspell, which is an XS interface to GNU Aspell.