How does Sundering Titan handle snow lands?
"Snow" is a supertype.  If you look at Snow-Covered Plains you will see that it's types are "Snow Basic Land - Plains".  Which means that it counts as a basic land and a plains.

So in the case of Sundering Titan, if there was both a regular Plains card and a Snow Covered Plains out, you could only choose one of them to destroy.

Relevant rules:
From the comprehensive rules glossary


  Basic Land Type There are five "basic land types": Plains, Island,
  Swamp, Mountain, and Forest. Each one has a mana ability associated
  with it. See rule 305, "Lands."


And


  205.4c Any land with the supertype "basic" is a basic land. Any land that doesn't have this supertype is a nonbasic land, even if it has a
  basic land type.: Cards printed in sets prior to the Eighth Edition
  core set didn't use the word "basic" to indicate a basic land. Cards
  from those sets with the following names are basic lands and have
  received errata in the Oracle card reference accordingly: Forest,
  Island, Mountain, Plains, Swamp, Snow-Covered Forest, Snow-Covered
  Island, Snow-Covered Mountain, Snow-Covered Plains, and Snow-Covered
  Swamp.


And from the rulings on Snow Covered Plains:


  “Snow” has no particular meaning or rules associated with it.


Also (emphasis mine)


  Since this is a basic land, you may have any number of it in a
  Constructed deck in any format in which the Masters Edition II set,
  the Coldsnap set, or the Ice Age set is legal.