In reply to NigeR:
Southern sandstone needs at least a day to dry out enough to climb on - means it is pretty much unusable this weekend?
There is a southern sandstone bouldering guidebook, but it might be sold out.
High rocks has lots of higher grade stuff but costs a tenner.
Bowles has the best quality rock in a nice compact area and costs about £3. Can be a bit of a suntrap in good weather, but is the quickest of them to dry.
Harrisons is free and has lots of rock, but the bouldering is a bit spread out and with a longer walk in.
Personally I think Bowles is the best, but you could make a case for any of them.
My top tip is to take a towel to clean your shoes ...