I second 99designs.com.

In fact, I will go so far as to say this: most design projects should begin with a contest at 99designs.

There are reasons for this: you get to see a large sample set of competing designs rather than being restricted to whatever designs the neural pathways of your dedicated designer can come up with. You go with 99designs in order to see 100 designs (or 500) sitting on a page. After that, you take one or two designs and you run with them. In my opinion this is bar none the most effective way to start any design project. Make 99designs.com your first step as it gives you a breadth of design options. Then choose one and work on depth and polish.

I'm not sure why this (and crowdspring) is voted down. For the initial phase of design or designing small parts (logo's icons, home page) a global marketplace of competing designers works very well.

When you have the design you can run with it - and if you actually want to develop a working relationship with the winner you can always do that.

There seem to be quite a lot of designers out there strongly opposed to 99designs and its ilk:

http://www.no-spec.com/