Stripe. We're hiring engineers in San Francisco, remotely within US timezones, and in London. INTERN, REMOTE, H1B all welcome.
We have a lot of awesome stuff in flight (not the least of which is our third Capture the Flag, which I'm working on as I write this post). See <a href="http://www.quora.com/Stripe-company/What-engineering-problems-and-challenges-is-Stripe-solving" > for an overview of what we're working on.
If you're interested, feel free to ping me at REDACTED_EMAIL.