I just moved back to Philly from Boston recently, and I've been eating my haphazard way through the city. Here's what I've found so far.
The food trucks around U. Penn: like the eggplant with garlic at Yue Kee (battered truck under Locust Walk bridge on 38th), though the Bejing hot noodles are disappointing--oversalted and not mixed well; however they are ready in ~5 minutes unlike most of the other dishes (~20 minutes). Eggplant with garlic has distinct notes of ginger, but unfortunately (as with most food truck containers) the styrofoam taste absorbs into the hot food. Definitely get the phone number to call in your order ahead of time, or be prepared to wait.
Pork bulgogi at KoJa at the intersection of 38th and Walnut is great as food truck quality goes; not quite hot enough for me, but I didn't specify. The dumplings that come with it are frozen-supermarket-bag quality.
Absolute favorite falafel truck is Rami's at 40th and Locust, not in the least because the owner always calls me "pretty young lady". Falafels are light and crunchy on the outside, but soft on the inside, and taste like 100% chickpeas. Great sour hot sauce.
Avoid the Mexican food truck on 33rd just south of Walnut. Really nice owner, but terrible beef burrito--mushy, homogenous, not even spicy.
Been to three different pho places on Wash. Ave. and can't remember the names of the first two, the third was Pho 75, which was not as good as the first two. First one was on a corner a few blocks east of Pho 75, and had great flavored broth, meat was just ok. Second place was just south of the first place and on the end of a row of shops (sorry, vague descriptions, maybe I'll find out names eventually) and had really excellent cuts of meat including soft well-cleaned tripe. Pho 75's meat tasted a little off, not going to head back there soon. While in the area, stopped by DiBruno's to pick up cheese--place was closed, but one of the workers on the sidewalk actually re-opened the shop just for my brother and me. Who says Philly people are unfriendly?
South St. Souvlaki has really excellent moussaka, creamy layers and great eggplant. Also recommend the appetizer sampler which includes hummus and tzatziki.
Heartily recommend my repeat favorites, Szechuan Tasty House (a.k.a. Fu Chuan Wei)--three pepper chicken, ma po dou fu, boiled beef, among many others--and Nan Zhou hand-drawn noodles.