If you really want a pistol with a light rail, I would recommend a Rock River Tactical
http://www.rockriverarms.com/item-detail.cfm?ID=PS2750&storeid=1&image=ptp.gif
or a Wilson CQB tactical light rail
http://www.wilsoncombat.com/p_cqb_tlr.asp
If an integral light rail is not a necessity, I would strongly recommend the Les Baer SRP or TRS. IMO, my Baer SRP rivals the fit, finish, accuracy and reliability of a custom-built pistol, exceeding the quality of the fit and finish of my Wilson CQB. At these prices, I believe that it is reasonable that the pistol will be constructed of the highest quality and best fit and assembled materials.
http://www.lesbaer.com/mono.html
I have not heard the best reviews of Kimbers, Sigs, and Springers, although I do not own any of them and certainly do not intend to be presumptive. I also do not own a RRA but have heard the best reviews. I own a Baer, a Wilson, and two Colts. My Baer and Wilson "were good to go" out-of-the-box. My Colts needed some TLC, and both ended up as base guns for custom house pistols. While the Wilson has been top-shelf, the Baer is nothing less than outstanding. Baers seem to be very reasonably priced compared to other limited production guns, and Baers and RRA are purported to be good values.
Obviously, there are several other excellent limited production shops out there, such as Nowlin, Nighthawk, and Brown.
If it were me, and I do not want to be pedantic, I would spend the extra money, if I had it, and buy the better gun. In my case, if I had learned this earlier, I would have spent a lot less money and been a lot happier with my purchases.
Good shooting!
N.B. The GSR frame is made by Caspian from Ruger cast blanks. Caspian produces some of the finest frames and slides on the market, and Caspian frames are guaranteed for life. I really dislike that absurd lock on the GSR, and I also prefer a Brown or Wilson padded grip safety to the Caspian padded grip safety on the GSR. Notwithstanding, another option is to purchase a Caspian light rail frame, with hand lapped frame and slide, and just about any option that you could imagine, including slide serrations, slide radius cuts, sight cuts, checkering, integral mag well, integral plunger tube, and a flattened serrated slide top and custom serial number, if desired, and have the pistol built by Ted Yost, et al, for a cost that would not neccessarily exceed that of a limited production pistol.
http://www.caspianarms.com/
http://www.yost-bonitz.com/index2.shtml
http://www.egw-guns.com/egw.htm