Seeing uncommitted transactions

Is there any way to look at the database as though you were inside another
sessions transaction?

I've had two cases recently where this would have been somewhat useful. In one,
a select into query ran for several hours and it would have been nice to
see that it was running correctly. In the other an application threw a
spurious BEGIN into the stream of operations, meaning that changes made
weren't visible to the rest of the world until it started another transaction
(which was ignored) and then committed it.

Cheers,
  Steve