Cameras, make a note when looking round, my dd nursery have a control room, where the manager tapes what goes on in each room and can look at 4 rooms in one go. Is the nursery clean, are the nursery nurse hands on, or do they just order the children to do things, are any of the children upset in anyway, if so are they being comforted, do you have to supply your own nappies, food etc or is it all thrown in with the cost. Also make a note to ask them, if you are charged for bank holidays (most nurseries do charge you, even summer vacations, this is to ensure your child keeps that place in nursery), otherwise exactly as bundle stated, honestly, I have paid over the top for a good nursery, or what I thought was a good nursery (thats a different story) that was brand new and when we moved, I had to find another nursery which was much cheaper, nearly 150.00 gbp per month and my dd loves it so much.
I knew straight away when I wanted my daughter to join the nursery which she is now at, it smelt nice, the staff welcomed her with open arms and when she was sad, they comforted her. The most important thing when visiting a nursery and I was told this a long time ago. DON'T MAKE AN EXACT APPOINTMENT, of course you have to ask them if you can come and visit, but arrange a time between certain hours, they like you avoiding feed times, but otherwise just say can I come tomorrow, don't ask them what time would be suitable, as they have time to cover things up (not all nurseries of course), but some can get rid of whining kids and mess etc etc. Good luck