Right now I'm between a Ruger GP100 4in, and a M&P 40 or 45. I have a M&P 9C and love it, so I'd like to add a big brother to the collection.
Nothing wrong with a Ruger GP100 or a Smith and Wesson K frame 357. I have them both and like them. You might take a look at a S&W 40VE sigma for a semi-auto. I have one and it is a excellent SD semi-auto. If you are fond of revolvers then you should not have a trouble with a Sigma. Double action only with a longer and heavier pull trigger. They are accurate and best of all you can buy one for around $350.
Good luck,
roaddog28