We have pretty similar question as a company.
We're a subcontractor to many big companies, and did quite a few unique things, we cannot talk about.
Rule number 1 - no matter how much you want to tell those stories now, remember, that you entered a contract and promised not to share names.
So, with this in our mind we do the following:
1. We describe the challenges for each project really carefully (if the challenge is way too unique, it may identify the project and the client, so you need to be really careful about that). We also say how we overcame those challenges and if the client was happy, how we compare to others and so on.
2. Then some clients would still ask for specific client names (from my experience - companies in the financial sector to this a lot). I tell them, that if I reveal the name - I am violating a contract with another client. And if I violate a contract with someone else, how can they trust me I will not violate their contract as well.
Usually this works, and it also shows your future client what they want to see:
1. Explaining the challenges and how you solved them should tell your employer / client, that you have the skills they need. Be specific here. Use domain language, so they see that you really actually are a rock star.
2. Explaining you are not about to violate a contract shows you're a person they can trust, and this isn't something common these days.
The above tactic usually works for us as a company and I believe if someone I am interviewing shows the same level of honor and skills at the same time he or she will be hired in our company right away.