Wordtracker GTrends is another quick, convenient, and free tool from Wordtracker.
This tool is a mashup of Wordtracker and Google Trends.
Punch in a keyword, like "fishing". You will receive a list of synonyms on the left and and three column table on the right.
The Thesaurus displays a list of synonyms. Click on any of those keywords and it will run an analysis for that keyword.
The Searches column shows an estimate of daily search volume.
The Keyword column displays a list of related keywords. Click on any of those keywords and it will run an analysis for that keyword.
The G column loads Google Trends for the keyword on that row.
This tool is an amazingly quick and easy way to analyze potential niches.