I just went to a really cool exhibit at the New Museum (235 Bowery).
The exhibit was "Unmonumental: The Object in the 21st Century". It consisted of art made out of mostly found objects. It's open till March 23rd.
If you go on the weekends, there is a sky room, which has a terrace with amazing views of the entire city.
http://www.newmuseum.org/exhibitions/4