If you plan to do some river travel then you need to travel in summer. I was there in October and that's definitely too late in the season. The river timetable is hanging in the river station or "retchnoi voksal".
We took the train from Tomsk to Krasnoyarsk and travelled 3rd class ie Platzkartni. Leaving Krasnoyarsk we took the Baikal Express to Irkutsk. For the Baikal Express you can only buy the tickets once the train left the previous station, only then it is known how many places there are actually on sale. There is no Platzkartni on Baikal Express as it's one of the best trains. We travelled Kupe.
It's worthwhile to jump on a ferry and go and see the city and its surroundings from the river Yenisey! The ferry is also how you get to the Dam (see my must see activity tip). I cannot remember the exact price of the ticket but it's not expensive at all.
The best, and probably the only way except for aeroplane, is to take the Trans Siberian train. Along the way the train will call at various stations and this gives passangers an opportunity to scour the platform stalls for local foods from the region. The Russian ice cream is great and is available even in the depths of winter.