Sunnyside Taco Truck
Someone on here said it's called Los Vagabundos. It's on either 41st or 46th under the train.
Recs, reviews? I go to De Mole all the time, looking for something new.
The good one is on the corner of 41st and Queens Blvd. I think the hours are something like 7:30 p.m. to 4:00 a.m. Good chicken tacos. Be sure to ask for "pickles" (picked jalapenos and carrots - hot! excellent!). There's another truck that parks on 46th, between Queens Blvd. and Greenpoint Ave., but other posters have said it's not worth trying.
El Rey del Oro under the 52St station is also pretty good. I can only compare it to the taco truck in Astoria (it's not as good as the truck in Astoria) but it's definitely a great option to have when coming home late.