A developer pimps his wares by 1) still having a portfolio of sites they've worked on, 2) being able to have a reasonable conversation, and 3) being competitive on price.
You have no idea how goddamn hard it is to find developers - they're generally terrible at any semblence of marketing. And I say this as someone who spent over $100,000 on a web development firm for my startup before I was able to recruit an internal team. Everyone knows about Pivotal Labs, but after that, it's all-but-impossible to know where to look.
Funny you should say that. How would developers market themselves? Generally speaking.
I tried some Google adwords for my freelance services and it was money down the drain. Granted, I am a lone freelancer so most clients would be looking for firms for their larger projects. But I would still be interested in the answer.
Screenshots of sites they programmed wouldn't be as useful as they are for designers. Clients wouldn't understand code snippets...