- Wordtracker – Paid – Wordtracker periodically compiles a database of over 330 million search terms. Updated on a weekly basis. All search terms are collected from metacrawlers Dogpile and Metacrawler. Free Option – available here.
- Keyword Discovery – Paid – Keyword Discovery currently collects search term data from over 180 search engines. The database contains approximately 32 billion searches from the last 12 months. Free Option available here
- Google Adwords External – Free – generates keywords from Google’s database.
- Keyword Country – Paid – Adsense keyword tool. There doesn’t appear to be a free option.
- NicheBot – Paid – Searches across Keyword Discovery, WordTracker and Google. There doesn’t appear to be a free option.
- Hitwise – Paid – Combination keyword research and competitive intelligence tool. Rather pricey, doesn’t appear to be a free option.