LinkCheck is a free software package that checks a web site for bad links.

Features
Understands HTML 3.0
Understands Frames
Understands JavaScript
Fast and lean, written in C. Source code is free
Can check a whole web site
Can be restricted to subdirectory checks
Estimates download times for each page and flags slow pages
Validates and reports temporarily moved pages and checks the new location
Reports server types
Reports html files last modification time
Validates mailto hrefs for valid DNS MX record on the internet
Validates ftp/file hrefs by getting actual file via ftp protocol
Reports news:, telnet:, wais:, gopher, powwow: urls
Automatically walks the entire web site tree