Another fine Roman spot to catch up on some jazz. The times I've been they've had more local preformers, but they've been really professional and it's great to hear how the Romans interpret their jazz.
The jazz room is upstairs and is possibly one of the squashiest, most amazingly comfortable places to see jazz performed. The space is tiny- most of it being taken up by the upstairs bar- but there are loads of couches and lounge chairs which give you the perfect oppurtunity to stretch out in comfort. Due to the lack of space you should try and arrive a little early if you've got a large crowd going or leave your chance to luck.
Being so close to the Spanish Steps it can feel like a bit of a showcase at times, but you don't have much opportunity to preen and primp at jazz shows so it's kept to a minimum. Gregory's is however an elegant place to listen to jazz.
You don't have to pay membership fees like in other places around Rome, but you are expected to buy a drink worth a minimum of 10 Euros or so. Luckily the cocktails are actually quite yummy and generously portioned. Try the strawberry capirinia. Yumm.