When it comes to keyword suggestion tools, there is a vast database of tools on the web, its almost impossible to list them all. One site which does try to list them all is SEO Company

Webmaster Toolkit - Excellant free tool with selectable search engine

Digital Point - a solid keyword tool

123 Promotion - generates a list of keywords based on your content

Global Promotor - another freebie tool that uses six search engines

Go Rank - interesting tool that generates synonyms based on your primary keywords.

Off course if your after the best keyword tool than you cant go past:

Web CEO has probably the best overall set of tools for search engine optimization around, and considering something like 130,000 people are using there software, you know your in the right hands.