Depending on your budget, you could go a couple different ways.
Sites like sortfolio.com can help you find some really talented people and firms. You can look locally, or just find someone who does work you really love. For the most part the companies listed are in business making websites and applications so you can expect the pricing to reflect working with a professional. It also means you can basically just present your idea, have them sign whatever assurances you’d like, and they’ll take it from there. Of course you’ll still have oversight and final say in what happens, but you won’t have to sort out the details, their job is to make your idea happen in a beautiful way.
There are also usually web development trade groups in most cities. I don’t know where you live, but Refresh is a group that’s in a lot of major cities, has monthly meetings, and at least the two I’ve participated in, also have a job board. Posting there might help you get in touch with the someone who’s available, local (if that’s important), and interested.
If you don’t mind staying on top of things a bit better and putting in some additional leg work, you can usually find students at a local college studying either programming or design who are into making web sites on the side. Designers usually know programmers that can make their designs into functional sites and programmers usually know a designer or two. Some folks do both. As I said above, I’d be more prepared to be involved on a regular basis if you go this route, but it can definitely save you some cash. This doesn’t have to be local either, you can drop an ad on craigslist in any college town and you’ll get quite a few responses.
I’ve worked with a couple folks from sites like getafreelancer.com or elance.com. They’re fine if you have a very specific task you want done and an exact specification you can pass along. I’m sure there are people there who are able to take a complicated idea alone and execute it wonderfully, I just haven’t had the pleasure of working with them. From my experience (4–5 projects), because price is so important to winning a bid providers bid the minimum it could cost to get the task done, and then do the minimum. There is no “art” to it, no advice on how to improve the idea, no frills or zip-zap, just the basics. On the plus side they’re always amazingly fast, so it’s great for a proof of concept, production work, or getting some expertise for a specific area of the project.
none of this is to say @poisonedantidote wouldn’t do an amazing job for you, just wanted to give you some info if that’s doesn’t work out for some reason… the best bet is always someone you trust and WANT to work with and it sounds like that may be the match
Good luck with the idea, let us know when you launch to fame and fortune.