There really is no point to buying a 4" 38 special revolver - you really won't experience any difference in weight between, say, a S&W Model 65 and a S&W Model 64. You will appreciate the versatility later.
I hereby vote for the following 4" revolvers, because they are all awesome.
S&W Model 65 or 66. 65 is the fixed sight version, 66 is adjustable. Both are K Frames.
GP-100. If you look around the auction sites, you can find the older 4" GP100's with the half-lug barrels - these are noticeably lighter than their current production, full underlug bretheren. You can also find some old GP100 4" models that have fixed sights and a bobbed hammer - they are double action only, 4" 357 Magnum revolvers that were a special run from Ruger for some police forces in Canada. I recently picked up one of these fine specimens on Gunbroker.com for only 295 dollars. EXCELLENT purchase. It was clearly carried a good bit, buy barely ever shot.
Another advantage to the GP100 is the 'grip peg' design - this allows for significantly smaller grips to be placed on the gun. This is also the reason why my fiance stole my GP100 and I barely ever get to shoot it any more. Eagle Grips makes excellent 'Secret Service' style boot grips for the Ruger GP-100.
Security/Service six. Excellent, older revolvers by Ruger. They have a full grip frame, similar to the S&W revolvers. They were made to compete with the S&W K-Frames of the days of yore, but they have one distinct advantage - they are stronger. K-Frames have issues with some magnum loads - noteably hot 125 grain loads. These bullets can slam into the forcing cone and crack it. Then you have a paperweight.