SEOggestor is a search engine optimization tool that looks up fill-in suggestions on five search sites: Google, Bing, YouTube, Amazon, Yahoo!, and Yandex (a Russian site). It takes as input the initial string of characters for a search and returns all the suggestions that would be provided by those sites to a user inputting those characters in a search query.
The idea behind this tool is that the phrases found using SEOggestor not only enjoy some degree of existing popularity, but will also drive new search users to your site if you capitalize on a specific, perhaps obscure suggestion (assuming the suggestion doesn't promptly disappear). Obviously this tool does not help with the heavy lifting of SEO, namely embedding those terms into your site in a way that manipulates search traffic, but it does provide a head start in figuring out what to focus on, somewhat independent of search portal. It does not look up related terms or synonyms, although some sites suggest spelling corrections, and this is reflected in SEOggestor's results.
Sam's Protip: Google has cracked down recently on sites that load their pages with more keywords than content. Ill-performed SEO can be a shot in the foot.