I would like to recommend 'Rank Checker' add-on for firefox. It is really powerful and you could select which engines to use and could require as many keywords as you like at one click.

Wish this help,

I suggest to use google webmaster tools from google. I think it's really acurate

Yes. You are right. Google WebMasters Tool gives the correct position. Also, you can get the result for the last 7 days. One another advantage with google webmasters tool is that you could check by which keyword people entered your website.

thanks for the valuable information

if you have hundreds of keywords that you will be input the plugin will query google yahoo bing and hammer their servers over and over until Google will start giving you a CAPTCHA and sometimes the first time you visit Yahoo will give you an Error 999.

I attended an event earlier this year where one of the break out groups discussed content creation for user experience as opposed to content creation for the search engines. I would say that unless you not showing up at all in the top 25 of google rankings for your keywords, try to put more emphasis on creating content for the user experience. When you do that, combined with solid SEO, you will never really have to worry about your google ranking again. I know this is probably not the answer you were looking for but I wanted to give you another perspective to consider once you are happy with your google rank when you find it.

the real story is that i am working to SEO my site. it is my first experience in this issue. i am try some new keywords and want to write down my site position in google frequently to check out these keywords are right for my site or not.
Google webmaster tools ,as i see,just say site position for searched words not for my site keywords.

Google analytic is a better way to do this, but I will suggest you to check your ranking manually.. because some of the rank checker tools don't give accurate results.

Maybe you can use http://www.ventio.se/seo-tools/google-position/ to check.