Keyword research is a vital part of internet marketing and many new marketers are always looking for free keyword research tools. Microsoft Adcenter Labs have a comprehensive list of various tools to assist you in your keyword research. Check it out. There are a number of different tools listed on the page that have different functionalities.

Ad Text Writer: Automatically generates text ads for an input URL.

Context-Based Acronym Resolution: Expand acronyms and abbreviations based on related search keywords.
Keyword Group Detection: Given a word or phrase, find a set of similar words.

Keyword Mutation Detection: Detect frequent misspellings or alternative spellings of the same keyword in search query logs.
Search Funnels: Analyze and visualize user search sequences in the form of funnels.
Search Result Clustering: Cluster a set of documents, such as search results, into semantically related groups in real time.
Forecasting Search Volume Seasonality: Forecast the seasonality patterns of search queries.
Keyword Forecast: Forecast the impression count and demographic predictions using one or more search terms.

Entity Analysis: Analyze multiple-word entities in a search query.

The tools provided are very helpful for conducting research, analysis and assisting with your Pay Per Click ad campaigns.