Lost Taco has a lovely entry about Tacos Xochimilco on 5th Avenue and 45th Street. The blog entry is also very complimentary to Sunset Park.
from the blog:
Sunset Park is charming. The park itself goes uphill to the East, and to the West you can see down the side streets all the way to river. It had just rained, or was just about to rain, so it was clear and bright and muggy.
He even makes mugginess sound "charming." Impressive. He is even more pleased with the food at Tacos Xochimilco:
With bravery and trepidation, I picked up the Carne Asada and bit in. The flavor was surprisingly good and the meat was actually juicy(!). Was that juicy beef and char I just tasted? I think it was. I took another bite. Each little meaty morsel actually had flavor and the protein was balanced perfectly with the generous cilantro, onion, and salsa mix. They even served their tacos on the tiny 3 inch tortillas that I like. (Although you have to ask for pequeno.)
It's almost enough to make a vegetarian try one of these tacos. Almost.
The more recent entry on the blog is for Tacos Matamoros, located almost directly across from Xochimilco. Matamoros used to be on the opposite side and down a block, but they moved to this more spacious location. They are still almost always full. It gets more attention than Xochimilco, so I'll leave you to discover the description for yourself.