I rode the Trans-Siberian 4 years ago. Technically, I guess I rode the "Trans-Mongolian," from St. Petersburg to Ulaan Baatar.
Anyhow, I recommend the "Trans-Siberian Handbook" by Bryn Thomas. The LP Trans-Siberian guide is also good. Both books have mile by mile descriptions of what you're seeing and where you are stopping.
I'm not sure what the schedules are like now, but four years ago the train stopped for 30 minutes in the town of Ulan Ude, near the Mongolian border. I saw from the guidebooks that the town square of Ulan Ude was home to the world's largest head of Lenin. And the town square is only about 1 km from the train station. So a Danish girl and I decided to leave our bags on the train during the 30 minute stop, run to the Lenin head, then run back. You would think this would be easy to do in 30 minutes, except that (a) it was late November and a throat-burning 5 degrees Fahrenheit, and (b) we didn't calculate that we would also have to run the length of the train to get out of the trainyard, as well as climbing stairs up and down leading over the tracks and out of the yard.
Anyway, we did it with a few minutes to spare, which included about five minutes for a few photos with Lenin. It was good fun, and I recommend it. Do it drunk if you want more of a challenge. Also, if you don't get out at Irkutsk, I recommend at least waking up early and watching the train go around Lake Baikal that morning, it's pretty impressive.