Ode to Xenu (link checking software)

This technically isn't related to spam elimination - but I'll include it hear anyways.

Xenu Link Sleuth is the best link checker I've ever used.

Xenu can quickly scan your website for any broken links and then report them in an intuitive interface. Alternately you can generate the reports in HTML format.

It also produces useful `optimization' related info, such as which pages are linking to which. It can even validate off-site links.

One of the most useful tools I've run into.

While some link checkers actually charge extra for their "enterprise" editions to handle more than a certain number of pages, Xenu has a single pricing structure.

It's free.

Resource: Ode to Xenu (link checking software)