Google AdWords does provide a way internally to get suggestions for keywords in your marketplace, its called the Keyword Tool. This tool is found when drilling into the account at the 'keyword' level. This means you have clicked past both the Campaign and Ad Group levels to display your keywords and ads.
This tool is free to AdWords users, so great right. Well in the past not as much because depending on what you gave the tool as a starting term for more suggestions, the tool spit out those suggestions from most general (least useful) to specific. Furthermore, the only information associated with these suggestions was 2 simple horizontal bar graphs detailing, 'advertiser competition' and 'search volume'. So hopefully your are following me in that no numeric data was given whatsoever.
Now Google has expanded the tool to return suggestions with 'approximate search volume' for the last month and 'approximate average search volume' with an actual value. Practically speaking, your campaign has only to spend a predetermined amount any way, so its not as if one regularly finds him or herself adding up search volumes, but it is nice to quantify what Google used to shove into a half inch blue bar.
When it comes down to it, we need to have all the necessary keywords in the PPC account regardless of search volume because we need to target what it is we have deemed necessary in achieving our projected goals. That is, we do the best we can with what we can in the given market with a given budget for a certain business model. But I can say it is significant that Google's Keyword tool is a bit more useful, and frankly it is nice to see Google sharing any real data with us at all. I'm sure tired of getting email replies that might as well have been some fraction of a bar graph. But Google must be listening to the people to some extent in changes as little as this one.