I've put a new paper online: "Two-Dimensional Semantics". The paper was written for the forthcoming Oxford Handbook of Philosophy of Language, edited by Ernie Lepore and Barry Smith. It's an overview article with a review of the two-dimensional frameworks of Kaplan, Stalnaker, Evans, and Davies and Humberstone, and a somewhat more detailed outline of the more recent sort of two-dimensionalism defended by me, Frank Jackson, and others. Connoisseurs who keep up with all of the recent literature won't find too much that's new here, though the final section on objections and replies might be useful. Those who are less familiar with these issues might find the article to be a useful starting point.
The article is a draft and I'll be revising it shortly. Comments (on matters big or small, either here or by e-mail) are more than welcome.