Despite seemingly everyone having a web product, it's borderline impossible to find someone reliable, who actually answers and who actually does the work to a quality that's above "I made a Tumblr." This leaves a lot of people falling into well-documented pitfalls associated with web development because you hired the wrong person or did a terrible job yourself. I'd put myself in both camps.
There's also a big advantage to doing external development. It's really easy to get stuck in your own head, and an objective perspective is exactly what you need to appeal to, well, your audience, who are most likely objective. I did some digging and, along with a few suggestions from professional contacts, pulled together places you can either outsource to entirely or find the right person to do so.
Toptal is known as a place for hiring freelance developers to join your team directly, but in 2015 they quietly started offering fully-managed projects for select clients. I've heard good things about their finished products, and they differentiate themselves by making sure to scour the top-level of freelance talent. Less than 3% of applicants make it to the pool, to the point that Fox Business covered how brutal you'll find Toptal's screening process. They can handle a lot of different tasks, somehow offering a network of thousands of senior web developers, designers, and QA specialists across 93 countries. It's a much more reliable option than most.
Acquired by EMC in 2012, Pivotal Labs is nearly twenty years old, well-known for setting a high bar for agile Ruby on Rails web development, Pivotal has also open sourced a series of testing frameworks and project collaboration tools, including the widely-used Pivotal Tracker. Pivotal Labs is a great solution if you have a few yet not quite enough qualified team members for the project you're working on. They'll work with and educate your team throughout the project, leaving you with a finished product and some extra expertise.
With a team of over 3000 across 13 countries and 30 offices, Thoughtworks came recommended based on quality and quantity, despite me thinking such a thing was impossible. They've also published an extensive list of open source solutions and have a strong focus on working with sustainability-focused and social and economic justice businesses.
NYC Dev Shop came highly recommended for Ruby on Rails solutions at fixed prices per package. Like plumbers, a lot of developers will enjoy pumping up contracts mid-flow saying they "didn't realize it was this much work." Apparently these fellows don't. They stick to agile methodologies, so customers report constant communication from the team and updates about the progress of the project, which, again, is very, very uncommon.
The Silicon Valley Software Group was formed by an illuminati-level selection of resumes, and specialize in entirely outsourcing web development. They effectively handle everything from rapidly building a minimum viable product to providing high-level technology architecture consultancy. They'll also audit your digital teams and make sure they're set up for long-term stability. They even provide a quick and dirty MVP calculator to provide you with a back of the envelope estimate for your web project.
Featuring a solid portfolio of well-designed and developed websites and mobile apps, Coalesce is a major player in the NYC web development scene. They specialize in delivering a great experience with an unique artistic insight to projects like their work for Prong. They apparently very much value the longer-term relationship with a client, so if you're going to be looking for a few projects over the next few months or years, I'd give them a ring.
Thoughtbot's team, spread across 11 locations in the US and Europe, has a fairly extensive history of open source contributions and an impressive GitHub page. Like many smart companies, they don't mind sharing their knowledge, and have published more than a few books on effective web development.
Neo's consultancy has a quirky pitch; they'll "build startups for your company." They look to bring the rapid-fire, liquidic world of startup development to whatever it is you want to build, yet for large companies like Paypal, Adobe and AMEX Open. They do far more than simple websites, building an entire solution like they did working with Time Inc, and while I imagine they're not the cheapest people to work with, they do seem to deliver.
Citrusbyte is sort of like hiring a mercenary group for the web, typically consisting of two software engineers, a designer, and a product manager dedicated to your project. They'll also onboard growth hackers, business and brand experts, architects, and many other things you're definitely going to need. It's like the A-Team, but online. Sadly, you can't hire them to be the actual A-Team.
Hashrocket is another Ruby on Rails-based web development firm with offices in Chicago and on the beach in Florida, which I'm very jealous of. They keep standards high by adhering to the vaunted pair (or peer) programming techniques in the collaborative style. In addition to providing prototyping, consulting, and development services, they also offer small-team training sessions for clients looking for a permanent talent upgrade in their existing teams. This is fairly important considering that, as you grow, you probably don't want to entirely rely on an external team.