In general, it's best to photograph/show the right side, because then you can get a quick look at how many screws are on the side and know instantly what you are looking at, but that's not really necessary here.
With that S/N and that hammer, it can only be a 1930s vintage M&P, 5" barrel it appears. Funny, theres a thread further down the first page of this forum with a lot of pics of 5" M&Ps in it, original post by StrawHat.
The grips look like 60s or 70s vintage herret 1/2 checkered targets (I think that is what they are) - looks like Rosewood I think.
I am guessing it's a .38 S&W special, should be on the right side of the barrel.
"Book" value on that is, in "fair" condition $135 with correct grips. Those grips are probably worth the same as some original ones, so we'll ignore that.
Book values (early 2006 update) are generally low because of appreciation lately, but on the M&P they are more accurate - they made so many millions of these over the years that they aren't scarce. I think they have made about three million total to date since 1899 when it came out.
the official name of that gun is ".38 Military & Police Model of 1905 - Fourth Change." During WWII it was made a little more cheaply and called the Victory Model. In 1958 it was renamed the Model 10 Military & Police. This could also thus be called a "pre- Model 10." I have one of these, a 1947 "transition model" that is much like yours - 5", pre-war long trigger action, etc.
They shoot well, the 5" balances better to me than the 4" or 6" - just a good solid gun. Don't use +p ammo, though - stick with standard .38 loads. If you want to sell it, use the classifieds here or an on-line auction like Gunbroker or Auction Arms.
If you want correct grips for it, send me an email and I can point some out to you. If I made any mistakes here someone should be by soon to correct it! Someone might have a better idea of current fair market value than me, but I think the book sounds about right on this one.