There is no denying the fact that the blogger`s best keyword research tool is his brain. First and foremost we rely on our industry expertise when writing up a post. However by using keyword research tools, you can both get a deeper understanding of your niche and audience and broaden your outlook.

1) Google Adwords Tool for keyword suggestions. This one is primarily meant for PPC campaigns, so you should definitely treat it with some grain of salt. Still, it does give you some (definitive) idea of each term popularity). I always have Show synonyms ticked to get more ideas, and I also like to play with sorting options. (To get keyword suggestions and all the possible info on them, I also often turn SEOBook`s wonderful all in one keyword research tool).

2) Google Sets to get more synonyms and thus enrich your writing style. This one not only allows you to get more ideas to expand your keyword list, it also shows what Google considers relevant.

3) Misspellings by MSN for you to understand how surfers tend to misspell your keyword. What`s good about this tool is that it seems to rely on actual users` behavior (not just generating common misspellings based on Grammar rules)

4) Find your keyword associations by searching eBay to make sure your key term / brand name has no negative or fixed positive associations (which, in both cases, could be rather hard for you to brand in both cases).

5) Define your targeted audience with MSN Demographics Prediction tool (also not very often used by me).

6) Google Trends to understand how popular your term is based on the location and/ or period of time. Recent Google Insights tool is another cool option to use: not only will it help you understand your keyword popularity but also list related phrases (most popular ones and most recent ones).