Found Diese Onze while out walking in the afternoon and made a mental note of where is was.
When we asked the concierge at the W hotel for a recommendation on a hip Jazz club he recommended "House" (lol 2 mins inside the door before we even got to the bar we knew House wasn't our kind of place and jumped into a cab to hunt down where we saw Diese Onze earlier in the afternoon).
Diese Onze is everything you want from a jazz club. It's downstairs in the basement, it has comfy tables and chairs that you dont mind hanging out in for more than a few hours, and has super friendly staff.
I reccomend grazing on the tapas menu; between the two of us we had 3 dishes and saved room for 2 deserts.
Although they only made straight up instead of creamy chocolate martinis the music more than made up for it.
(I've uploaded a short video clip here - http://deancollinsblog.blogspot.com/2009/10/diese-onze.html )
Met some super friendly Canadians who we got talking to about Australia and living in NY etc - all in all the night couldn't have been better.