Question: I am especially interested in data input ergonomics: keyboards, mice, and chairs, but would also like to hear about other ergonomic improvements that changed project performance. References to specific research, case studies, or best-practice sheets would be greatly appreciated.

The question is: Do ergonomic keyboards, mice, or chairs make a difference in delivering projects on time, on budget, or according to spec?

Answer: 
This question is applicable to project management as it is in all other types of operations, whether it is knowledge type work or labor. The application of the science is through generalization of the findings versus a study that shows a direct correlation between a project optimized ergonomically and one that is not. 

The challenge in answering this question is setting expectations that you do not have a cause and effect between an egonomic station and cost, schedule, and scope performance. There are an infinite number of variables, including a host of uncontrollable, random variables, that ultimately affect where we end up with cost and schedule and scope quality. Our jobs as project managers, and operations managers for that matter, are to increase the likelihood of favorable results by pulling the levers and pushing the buttons that are known to help with the full understanding that you still have risk of poor performance and complete failure.

Googling ergonomics and performance yields a host of scientific findings that suggest improved musculoskeletal and visual performance via lack of symptoms or employee complaint. One could easily conclude that, in most cases for much of the time, performance should be improved by providing ergnomic work stations. 

Personally, I do not think there is much debate around this topic so I would certainly include an ergonomic work station and environment, and the cost thereof, in my project planning. While the results are no where guaranteed, no magic bullet, these are the right levers to pull to help increase my odds.

Two studies:

Health and Performance Consequences of Office Ergonomic Interventions Among Computer Workers, Michelle Robertson

Office ergonomics training and a sit-stand workstation: effects on musculoskeletal and visual symptoms and performance of office workers. Robertson MM, Ciriello VM, Garabet AM.

The abstracts are available online; however, you might have to pay to see the entire study.
TL;DR
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This question is only indirectly related to project management, and isn't answerable in the way that you're asking it. In addition, requests for off-site resources or search-engine type questions are always off-topic.

That said, perhaps a valid answer is to simply point out where your question tangentially intersects with Project Management, and where it does not. With that in mind, I offer you the following guidance. 

Applicability to a Project
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While productivity is something that might concern a project manager, ergonomic equipment is more of an HR or facilities issue. The real impact to the project would generally come in the form of:

1. Process issues, such as whether team members can request ergonomic equipment and the procedures for doing so.
2. Budget issues, such as whether such equipment is a cost to the project or to some other organizational unit.

Ergonomics as a Science
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It seems like common sense to say that if you don't have people losing working hours to back pain or carpal tunnel syndrome then you will avoid preventable losses to productivity. If, on the other hand, your question is more along the lines of "How much faster will my programmers type if I get them ergonomic equipment?" then I think you will need to turn to research literature.

Setting aside people's physical comfort and required accommodations, in my experience people on knowledge-based projects spend more time *thinking* than they do typing or mousing around, so my expectation would be that any real productivity improvements will come from the health and happiness of the team members rather than from any measurable improvement in systems input.