In preparation for RTW trip I'm looking for websites or other information sources for rail routes in South America, Indian subcontinent, Turkey, and Laos, Cambodia, Vietnam.

Re India
Do you mean with maps? Good luck!
Have you found the official govt booking site. irctc.co.in If you have a decent map with you, when you enter your journey, you can also see the route. But this is obviously a slow way to figuring out which train trips you want to make. The easiest way, I think would be to buy a decent map or see if the library has one. I have some good maps (nelles) and can help you out a bit if you have specific questions.
Also have you found the site of the man in seat 61. If you google in some of that, or put it in teh search engine on the india branch, it will turn up.
Steven_ber on here and IndiaMike is also an excellent source of info about trains.

Greetings,
Turkey you will pretty much use the Bus system which runs great here is a site about the bus travel. http://www.turkeytravelplanner.com/trans/Bus/index.html
Cambodia is pretty much just buses that you book through the local travel companies.
I found this site for Vietnam:http://www.vr.com.vn/English/hientai_hoatdong_hanhkhach.html but most of the time you just book through your hostel, hotel or the million tour agents that are around.
Hope that helps.
Onesweetearth