For downtown Mahattan shots, especiall at dusk or night, you can either walk the Brooklyn Bridge (a great experience in itself - good thing you've got it penciled in) or either walk or take a train to Brooklyn Heights and take shots from the Promenade...
The very best shots can be had from the Staten Island ferry, from which you can also get good shots of the Statue of Liberty, if you're into that sort of thing... of course the ferry is moving, so an IS camera or lens helps...
If you like sunsets, try going over to Jersey in the evening. Sometimes the sun reflectsquite nicely in the Manhattan skyline...
---
For street action, nothing beats the Lower East Side, IMO, but I'm biased - I live there.