Keyword research platform Keyword Discovery (a service of Trellian) announced a professional-level plan today and it’s worth a look.

Under KeywordDiscovery's professional plan; search marketers have the ability to set up unlimited projects and will receive:

- a Competitive Intelligence (CI) subscription to monitor a competitor's referring traffic sources, natural search queries, paid search terms, ranked terms, and subdomains,

- access to an expanded version of the Domain Researcher Tool (useful in finding which domains are registered, available, or for sale, based on keyword research).

- access to a stand alone version of the Keyword Cross Reference Tool (which enables marketers to enter a URL along with target keywords, and view a breakdown of those keywords on a competitor's webpage),

- access to a stand alone version of the Keyword Permutations Tool, which enables them to enter a list of comma separated keywords and view all combinations of those keywords that show up in KeywordDiscovery's massive database of searches.

Other professional level features and tools includes Keyword Density Checker, access to the Keyword Management Tool to filter and manage keywords, and access to Yahoo PPC Bid values for checking current pricing for keywords in Paid Search.