what is in your experience really really cool, and details please – maybe we can learn something.
This is not strictly in the BDSM line of things but someone I 'knew' loved the alternate sensations of hot and cold while getting a blow job, the secret is a hot cup of something (tea, coffee, Water etc) a couple of ice cubes and of course teeth that are not sensitive!!

The alternate sensations of hot and cold used to drive him absolutly wild!