There is some great stuff here. There is one important thing missing from (nearly) all of the answers you have been given, Dan.
How you deal with this has everything to do with your long-term strategy as a company, and how your product roadmap fits into it. If you don't have a strategy, and you have a million requests flying at you all the time, it's extremely dizzying and frustrating to try and prioritize everything. You can make your 2x2 grids, and so on. That method works for situations where you have a good idea of the value and effort of each request. But it doesn't help move your company towards its goal.
[And, to deflect the immediate immediate objections from the Agile/Lean crowd (of which I am a member ;-) ) you absolutely can
balance validating your product-market fit with data, AND have and pursue a long term vision.]
I have this problem you describe now, and I have had it as CTO at other companies. It's surprisingly common for the tech business, particularly with generalized platforms or solutions. If you have good product manager, this is what they live for. If you don't, you will likely have to be product manager until you do.
I actually did an interview with KeenIO's founder who talked about being pulled every which way in the beginning, when what they really wanted to build was a niche-free general solution. They managed to avoid it in the end. But I think you're in danger of those same distractions.
You and your CEO presumably have a long term vision for the state of the world in the future ("where do you see yourself in 5 years, blah blah?"). And you have your product now. How you bridge the gap between your current system and that vision is your strategy. You can change your strategy over time. You're not always going to have the right strategy. But you have to at least have some strategy.
Then, you need to ignore anything that does not move you forward toward the vision, even if it looks big and shiny. Your job as CTO is not to fulfill orders from customers like a cook. It's to build a system that fulfills the mission of the organization. If your CEO doesn't understand that, you have some expectation setting conversations you need to have.
That said, there are times when you have to set things aside for revenue reasons, and just do one of the darn one-offs. You just want that to be the exception to the rule, not the norm. Make sure it's clearly scoped and well-priced to compensate for the opportunity cost of not moving your vision forward.
I'd love to chat with you, or anyone else, about this more in real time (coffee, video chat, or whatever).
Good luck, and we're here to help you! :)