Hopefully some entrepreneur out there is working on precisely this.
I've had the same thought over the past few days. This marketplace is a mess, but it would take me a month to build anything better.
Well, somebody (with PHP skills at least) want co-op in finish a project I've somewhat "hanging around" for about a month?
It's called bcommerce and it's an ebay-like site able to buy and sell (you can actually create an ad to sell carrots or an ad to buy carrots).
If nobody is on, well... wait one more month or so and I'll be on it again.
As long as people are actually working on things, good. Bitcoin NEEDS this kind of backing and attention or it will fail, no question.
This website may be of interest to you:http://www.bitcoinsreview.com/
It kind of does what you are wanting. Basically it will list all places where you can use Bitcoins for goods or services. User-reviews will show you whether the site is legitimate or not. It's still in it's infancy, just need to get a good user base.
There is a forum post here:http://forum.bitcoin.org/index.php?topic=9245.0
This is a step in the right direction. Please, ask for as much help as possible for your project. I do not think there are any other sites as well put-together for this purpose as this one.