Those sites do exist in a way, but you have to do the customer acquisition work yourself.
There are many technical forums where people ask "how do I do X" or "can anyone help me with Y?" There's often opportunity there to provide a paid solution. Sometimes it's explicitly asked for, other times you have to find out if the poster is open to paying for a solution.
I've been doing this for a while and I generally pick up a few small projects each month, but it takes some time before you get good at seeing which ones are real opportunities and which are just people looking for DIY guidance.
I suspect that if a free site to do this were to emerge, it would quickly end up with the same issues as eLance, Freelancer.com and the rest: race to the bottom on price.
To more specifically address the OP's question: in the past I tried using RentACoder for product ideas by datamining the job postings to see if there was enough overlap in requests that would indicate a product need. Never came up with anything concrete that I wanted to work on :-(
There are many technical forums where people ask "how do I do X" or "can anyone help me with Y?" There's often opportunity there to provide a paid solution. Sometimes it's explicitly asked for, other times you have to find out if the poster is open to paying for a solution.
I've been doing this for a while and I generally pick up a few small projects each month, but it takes some time before you get good at seeing which ones are real opportunities and which are just people looking for DIY guidance.
I suspect that if a free site to do this were to emerge, it would quickly end up with the same issues as eLance, Freelancer.com and the rest: race to the bottom on price.
To more specifically address the OP's question: in the past I tried using RentACoder for product ideas by datamining the job postings to see if there was enough overlap in requests that would indicate a product need. Never came up with anything concrete that I wanted to work on :-(