You can find graphic artists at very reasonable rates on elance.com (be sure to check their ratings)
I would advise however that you also consider working with a UX designer who has experience with the design of navigation/workflows and who understands usability best practices. Having a well designed and usable (intuitive) product will make your product stand-out and will make users more likely to enjoy the experience and return for more. This is especially true when it comes to social apps. I would also advise that you make it easy and enticing for your users to leave feedback. This feedback will be the key to understanding and identifying their needs. Then you can consider how to best meet those needs (if possible with the help of a UX professional).
Here is some great advice from a successful start-up founder:
http://www.slideshare.net/missrogue/the-10-mistakes-ive-made...
I didn't mean to imply that I am picking a partner to satisfy YC....that never crossed my mind! However, I highly value the experience and advice coming from YC partners, therefore, the fact that they place such high importance on having a technical co-founder made me question whether I needed to add a 3rd partner if the two of us don't cover enough "technical" ground. That being said, I now have a new question. I have officially made the partnership with her and I'm so excited about it! I just don't think I could possibly have a better partner. She is as motivated and hard-working as I am and we're up until 1AM every night working on our company. The problem is that I would like to add her to my YC application and I can't access to it anymore. What's the best way to get the message to YC?
The dilemma is deciding whether to take on a business specialist partner (with all the right qualities) and hire out the development, or keep looking for the perfect match in a technical co-founder. I have many hacker friends who are ready to pitch in and I trust them. We've worked together for many years. But no one that is in a position to leave their day job. I do have a few leads through my network and am still scoping things out. I wanted to get insight from this forum though and glad I did.
Thanks, I appreciate those answers. It definitely makes sense to be an all-in-one team. I am leaning towards learning the additional skills I need. Another option is to complete most of it and hire a developer to complete the rest. What's your perspective on getting the product completed in DHTML and then hiring a developer (a developer friend) to build the .NET Framework with SQL Server backend?