Isaac Asimov's "The Black Widowers" short stories are very rationalist, especially the character of Henry the waiter, who often exemplifies the principal of Occam's Razor. That is, when the rest of the group are coming up with wild and convoluted stories to explain the facts, Henry is usually the one to come up with the simplest and most obvious solution. Some of the stories are a little Holmesian (i.e. superhuman powers of deduction) but many are just a question of looking for prosaic ordinary answers instead of going overboard with speculation. In this vein, I particularly recommend:

• The Acquisitive Chuckle
• The Obvious Factor
• Northwestward

All three of these are collected in The Return of the Black Widowers. "The Obvious Factor" in particular taught me a really important lesson in rationality I've used with significant effect over the years. It took me somewhat longer to learn the more subtle lesson of "Northwestward"--indeed I'm still working on that one--but if anything it's even more important.