Tears of Serra
2W
Sorcery
Destroy all non-basic lands
Now, this is obviously very strong. There are three main points of conjecture that I can see being rased:
1) Non-basic hate has traditionally been in red. Despite this, I see no reason why white can't get it. Mass destruction is white, and the idea of cleansing non-basic land is pretty white.
2) The name. Well, rain of tears destroys land, so why can't the tears of a planeswalker destroy a lot of lands?

3) The casting cost. This is where I would like to see the discussion. I costed it at 2W as that is the lowest cost I could possibly imagine this card might ever get printed at. It will not be hard to convince me to raise it, for several reasons:
a) This is potentially stronger than Armageddon since it is a lot easier to make this a one sided 'geddon.
b) More limited land destruction such as cataclysm and global ruin have always been printed at CMC 4+
Note that this would probably never see play in vintage unless costed at 3 or less CMC. Note also, that this would probably see a lot of play in WW and WW/u in 1.x even if costed at 2WW.
The fact that it wouldn't see play in vintage unless costed at 3 isn't a really good factor in my view, since at 3CMC it could probably do disasterous things to the 1.x metagame.