The Santa Lucia restaurant in Chelsea has the best tiramisu I have ever tasted, and I've been around. Seriously, if you never tried it, go there and order them now!
I went on a Friday night and the restaurant was pretty crowded. I had made reservations, just in case. It was a really great experience. This is my favourite local place, because they cultivate such a feeling of warmth and community, and I absolutely love this little place. It's so cute and quaint.