I second recommendations for Lemongrass (Thai) and Rangoon. I'll add that Lemongrass is especially easy to park by if you're driving.
I am also a big fan of Sitar India, Bitar's, and Pattaya, but they may be a little too casual than you're looking for. Especially the first two.
In Chinatown Rangoon has awesome Burmese food. I love the Spring Ginger salad, Tea leaf salad, string bean and potatoe salad, Chicken Keema, Glass noodle salad.... actually I like everything on their menu.
Also in Chinatown Ong's on the corner of Race and 11th street makes excellent Vietnamese food. I also love Vietnam Palace.
Chinese is also a good choice. There are so many good places. Tai Lake, Sang Kee are good for cantonese style food. There is authentic Szechuan food at Chung King Garden. The freshest of soup dumplings and hand made noodles, Shanghainese style (and no atmosphere whatsoever) there is Dim sum Garden.
In South Philly at 11 and Washington Cafe de Laos has Laotian and Thai food and it is so good!
Aqua at 7th and Chestnut is nice for upscale Thai and Malaysian food. There are also two Malaysian restaurants in Chinatown, Banana Leaf and Penang.
Of course when you say best ethnic food in Philly that is a matter of taste and opinion. There are too many choices. Authentic Mexican , Korean, Japanese, African, Spanish, Portuguese, Philipino, Russian, Polish, Israeli, Brazilian etc...
They are from Indiana, not India. I think Rangoon is a great suggestion, but it would really be helpful to have more information, as there are so many options here. What price point? What do you mean by ethnic? Are you looking for funky hole-in-the-wall type places, or more upscale?
Philly has some Thai places, but nothing great. Banana Leaf is good for Malaysian. Shiao Lan Kung is great for Cantonese, Szechuan Tasty House for Szechuan. There are some great taquerias around the Italian Market area (search the board for lot of ideas) if you are wanting Mexican. There are good Vietnamese place in both Chinatown and the Italian Market areas. For Portuguese, there are good places in Northeast Philly. Port Richmond area has great Polish food. You get the idea...help us narrow it down and we can help you better.
re: Hungryin theBurbs
You are correct, not many good Thai Restaurants, however, you should try Loatian in South Philly.
Very similar to Thai.
Cafe de Laos:
1117 S 11th St
Philadelphia, PA 19147
Lemon Grass (West Philadelphia)- I think is the best in town.
3630 Lancaster Ave
Philadelphia, PA 19104
Korean in Cheltenham and in the Greater North East.
I think you should be a bit more specific. What part of town? Price range?
Technically, Italian is "ethnic", and we've got some non-Olive Garden varieties.
If you want to try something in the Thai vein without being quite so "normal", there's Laotian at Cafe de Laos.
Get back to us and we'll help you out. There's about a billion ethnic places. Oh, and are you going to drive or do you have to take public trans?