Tim Jowett and I have just published a paper on single-fit bootstrapping, which provides a simple means of calculating a confidence interval for a non-linear function of model parameters. The idea is not new, but we thought it should be more widely known, as it is simpler and more reliable than a Wald interval based on the delta method. You can find the paper here, and the slides from a talk on this topic is here.
David Fletcher Consulting 