For NY, i thought the boat around the statue of liberty and ellis island was pretty cool, but ellis island itself was kinda disappointing. If i had it to do again, i'd probably skip that part and just enjoy the boat.
If you're a foodie:
In new orleans Peche was a GREAT restaurant. It's won some awards (James Beard for one) so it might be harder to get into than when I left. I liked Mr B's Bistro too but i think it was a bit more expensive.
For new orleans, many of the "landmarks" i found to be pretty disappointing, such as having a Hurricane at Pat O'Briens. It was like oversaturated coolaid with rum. Venture just a few blocks off of Bourbon St and its MUCH nicer. Bourbon street always stank: In the morning they're washing away all the vomit so it smells bad, in the afternoon the water hasnt quite dried yet (it's very humid there) so it smells a little like mildew, and then in the evening it smells like vomit again! But there are some cool jazz bars and places that dont specialize in cheap Jell-o shots around, so explore. There are lots of famous cemetaries that are fun to explore with their mausoleums, and the architecture around town is wonderful. We spent one afternoon renting bikes and just exploring the city on our own, which was pretty cool. Its totally flat so the biking is easy.