Queens Tech Meetup has taken off as well as the Enterprise Tech Meetup.
There's a lot of smaller (<100-150 people) meetups organized on specific topics (cloud, languages, industries).
This week is @shakeshack 5 (recap of year 3: http://www.thisisgoingtobebig.com/blog/2010/10/4/shakeshack-... ). Unsure how to get into it.
The guys from Harvest have organized a startup walkabout, usually in the Spring.
Many startups host office hours as well (with varying degrees of openness to the public).
The other thing to do is: if there's something you're interested in and don't see an existing (or upcoming) related event, post to NYTM or NextNY that you want to organize it but could use some help (space is always a pain).