Like others here, I'm sure, I saw an episode of Alton Brown's TV show recommending a 'quarry tile' for use as a baking stone. Having checked Homebase (DIY store) I found the following:

Standard Paving stone (materials unspecified - looks like reconstituted something or other)

Limestone Paving

Sandstone Paving (I get the feeling this would be a baaad choice)

Bricks (common garden variety)

Which (if any) would be the most suitable for placing in a (domestic) oven?