My all time favorite is the sour cream coffeecake from Zingerman's in Ann Arbor, and I haven't had anything nearly as good in New York. If you know a good one, please share!
Not exactly sure of name but something like Grandma's Favorite Coffee Cake. I have bought it by the slice in Manhattan at Guy & Gallard (take out shop), whole via Zabar's and also online. Many varieties but I like the original or apple. My cat likes it too. Don't ask.