The Deck - http://decknetwork.net/ We received roughly 4300 uniques across 2 weeks. We got about 9x the clicks from daringfireball than any of the other sites in the network (37signals, A List Apart, Kottke, FFFFound, etc.) If you email them they are open to negotiating.

Fusion Ads - http://fusionads.net/ Very similar model as The Deck. We ran one of the $400 one-week "bursts" that they offer. Received about 1400 uniques.

Before we ran either of these campaigns we experimented on Facebook to see what sort of graphic/copy produced the greated CTR. We found that a very simple graphic, and simple copy always did the best.

After we ran the campaigns we also realized that Facebook advertising is a great deal. You can run really targeted ads on FB for cheap and get great results. I would definitely experiment here before spending big money on one of the larger networks.

Regarding art/copy, I would see what you can come up with on your own. Unless you're running a massive campaign, not sure a designer/copywriter is worth the expense.

Finally, it should be mentioned that a clever blog entry or two can generate far more traffic than a banner ad campaign.