Not sure what your plans are for using these related keywords, but yes, the Google Adwords tool shows lots of related terms. Different settings will show vocabulary with different kinds of relationships.
Both Google search and Bing search show related searches on their results pages... Google at the bottom of the page, and Bing at both the left side and the bottom on page one (and part way down the page on page two, etc).
The auto-complete tools of various search engines (include YouTube in this) also show what can be considered "related" keywords.
I'd also study the sites of successful competitors for ideas about what they target.