Google Insights for Search is a great little tool to help gauge interest.
Here are the highlights. First, point your browser to: http://www.google.com/insights/search/ Type in a search term that you might use if you were searching for your product. The results basically give you statistics on searches for this term. They can be broken down into category (by industry or market), timeframe or geographical location. You can also use the tool to view related search terms.
For example, plug in the term "child's guitar" and you will see that the graph shows huge spikes in November and December for the last five years in a row. It's a good bet that this is a popular Christmas gift.
Contrast this with the results for the phrase "guitar lessons" which shows a bumpy, but steady decline over the last five years along with flags from events in the news that contain the same phrase (for example, Lindsay Lohan apparently wanted to take guitar lessons from Slash this August).
If you assume that much of the time when people are interested in a certain type of product, they will "google it", then you can use this tool as a gauge of interest in your product.
Let me know if this helps.
http://www.limesurvey.org/ allows you to also do alot for free. Once you get more than 25 responses/month you need to pay them something fairly reasonable.
Another great free market research option is to go to Facebook, try to create an ad, and target the demographic as much as you can. Before charging you, facebook will give you an estimate of how large your target audience/market-size is.
Create an Adwords account. You should be able to get $50-$125 worth of Adwords for free. Now you can put up different types of ads and see if people care enough to click on what you are looking for.
We've been using SurveyMonkey and we found conducting individual surveys is very time consuming. You'll have to bug every one of your friends/family. You'll do well if you can get 100 responses.
The magic number for a statistically significant sample size is 500-1000 - that's when investors will start paying attention do the results.
Another method is to just roll out a beta and see if you can gain traction. Iterate as you get feedback.
On a side note, if you ever want to sell to the Chinese market, use http://index.baidu.com. It's much more robust than Google Insights/Trends. It even breaks down by gender, age, profession, and education level. Of course, you'll have to learn Chinese.
Brake, One of the fastest things you can do is to setup a survey using tools like (http://questionpro.com (go for the free subscription) and setup a simple questionnaire and send it to family, friends and coworkers who you think can provide some insight into what their thoughts on the idea would be.
It is important to ask specific questions like -
Would you be willing to be my early adopter if I had a service/product based on the idea?
Would you be willing to pay for this ?
I am not aware of any tools to do the kind of market research you are talking about.
For each idea, you need to look at existing competitors, understand where the market is under-served, and what the potential could be.
I don't believe you can automate that.
It's all highly dependent on how smart you are as well. If you asked people on Mechanical Turk to do that kind of research for instance, you'd get completely bogus results, because they wouldn't understand the subtleties of your ideas.
For other people, your ideas are mostly indistinguishable from existing products (especially on the web). Only you feels that existing solutions have shortcomings.
So roll-up your sleeves and do some good old fashioned research with Google, CrunchBase, etc.