I personally like #92 as well as #22, both north-south or, like we locals refer it to: sea-to-mountain. Also #150 can be interesting. Check http://bit.ly/vullanar and choose "Bus", you'll be able to plot the different lines in the map.
Never know what you mean when you say 'ethnic' sorry, as this term has different meaning for different people. Also, something that can be ethnic for you might not be for me... (ethnic cuisine as in "foreign" is Burger King for us, hahaha!)
Anyway, some ideas for international cuisines of the top of my head (just a small sample, eh!):
Thai?... three great ones in www.thaibarcelona.es , www.indochinelyleap.com and www.restaurante-thai-gracia.com
Fish and seafood (affordable!)?... www.laparadeta.com/marisqueria-la-paradeta-born-barcelona.html
More Mexican? www.tlaxcal.com or for something informal www.cantinamachito.com -which includes Chido One too.
Japanese? I love www.kibuka.com in Gràcia
Argentinian (meat lovers)? www.nuevereinas.com/en/ -but it ain't cheap!
Taste of Ucraine? www.timeout.com/barcelona/restaurants/yalta-crimea -unassuming, very homy.
Syrian? Ugarit, it's a chain and is cheap yet quite good. Plenty of them in Gràcia: www.restaurantesirio.es
Castilian (another meat lover's paradise)?... and superb surroundings: www.asadordearanda.com/en/restaurantes/barcelona/001/ --there are several in town but I prefer the one here in Tibidabo Avenue. Spectacular if you go at dusk: http://bit.ly/Zu5RBV Bit up-market yet not 'unreachable'!
Cuban? www.habanavieja.es used to be 'all right' -not great though- enough to taste a bit of Cuban food if you catch my drift.
... and then the traditional top-end ones... but I guess you can find those yourself in any reputable guide :))
Have a look at the 'bible' anyway: www.timeout.cat