Bogstad.v/hegdehaugs v.:
Voga, bogstadv. 1: Vivienne Westwood, Marc Jacobs, Tsubi, April 77 etc.
www.voga.no
Kamikaze Donna: YSL, Prada, Gucci, Cavalli etc
Sole Service - Sneakers. Vans, Adidas, Marc Jacobs Vans etc.
www.soleservice.no
KOMA (inside a bigger "department"store (not a department store, but i guess it looks a little like it) called Tatler) - Diesel, Fifth Avenue Shoe Repair, alot of vintage, etc
M.A - Balenciaga, Ann D, Rick Owens, Marni, Miu Miu.
MaxMara - Sportmax & Maxmara
There's also a really good vintage-store called "Tonica vintage" , but it's very hard to find, as it's "hidden". I think the street is called Schonings gate / street, or something similar, but i'm not sure..
This is def. the best area, but i guess Frogner and Grunerlokka has some OK shops to. I would ditch Steen & Strom as they sell mostly basic clothes, except for store "Norway designs" who carry, obviously, alot of Norwegian designers.
If you're interested, Oslo Fashion Week is next week (starts at 12th or 13th, i think) and i think you can get tickets. I'll be there
If you have only 2-3 hours for shopping, i would stick to bogstadveien (vei = norwegian for street).
Hope this helps.
Edit: I've got some adresses:
Vóga AS
Bogstadv. 1, 0355 Oslo
22 69 07 60
Kamikaze Donna AS
Hegdehaugsv. 27, 0352 Oslo
22 59 38 45
Sole Service
Oscars g 19, 0352 Oslo
22 59 44 11 (they got several stores in Oslo, so i'm not sure if this is the one close to bogstadv.)
Koma
Bogstadv. 11, 0355 Oslo
23 20 23 23
Max Mara
Hegdehaugsv. 23, 0352 Oslo
23 33 03 10
Tonica Second Hand
Schønings g 14, 0362 Oslo
22 60 22 06
Unfortunately, i was unable to find the adress for M.A, but it should be pretty easy to find.
This is btw the information-site for oslofashionweek:
www.oslofashionweek.com , if you're interested.