If you're looking for a Web application / site development consultant who "gets" responsive web design, I have a suggestion.
I was re-reading my notes from attending an excellent Build Right, Build Repsonsively workshop, and I remain impressed. I am impressed on the substance of the workshop. I'm impressed on the examples given and the thoughtful approach.
And I'm impressed by all the details of the experience.
The doing Agile without making a big deal about Agile, the caring about the quality of the product, the honesty, the attention to detail with self-awareness about where that point of diminishing returns may be reached, the attitude that doing it right and responsively doesn't cost extra, it's just the cost of doing it. I'm impressed that the President of the company has substantive technical things to say and is directly involved in the domain and work of the firm.
I love the attitude about training, that training is a central offering of the firm, an important activity, that by teaching it you learn it better and hone your craft. I love that their interns are expected to learn, not to do billable work.
I love that they have these thick, plastic, different business cards, because the President had the good sense not to micromanage what sort of business cards they ought to have, delegated the task, and delegated the authority to make tradeoffs as the delegate thought best. I hope I'm not so shallow as to be impressed by plastic cards, but I'm always impressed by finding great people and empowering them to do great work. And they are really nice business cards.
I don't want to overstate my endorsement here -- I don't have actual experience with Sparkbox consulting on anything, and of course someone closer to real actual projects with all their tradeoffs and nitty gritty is going to know much, much more and have a much more informed opinion.
Nonetheless. From my brief experience, from the totality of a bunch of positive, promising details, I'm left hoping for an opportunity to get more familiar, I'm left hungry to attend another of their workshops, and I'm left with the impression that this is a consultancy doing righteous work.