There are thousands of keyword tools around. And I'm sure you will get lots of recommendations by other members.
But if you only want to see search volume and you want it for free, there is one plugin I can highly recommend: Bing Ads Intelligence by Microsoft.
It's an Add-in for Excel, and I like that I get all the raw data right in there for further processing.
Now, the health warning: the absolute search volume numbers for Bing are lower than those for Google, and if you're in a country where Bing/MSN doesn't play a big role, the difference might be very large.
But I use them as relative indicators to decide on a short list of keywords. I can then always check the final list manually on Google.