We’re located right in the city center, in a lively coworking space called BeCentral.
(10 Cantersteen street, 1000 Brussels ) 

Regarding neighborhoods, the city center, Ixelles, Saint-Gilles and Etterbeek are nice but remember that Brussels is a small city, so luckily nothing is ever truly far away. 
We have collected a bunch a website that can help you...

Short Term 

- Spot A Home (min. 3 months, ask us for a discount code of 15%)

- AirBnB (of course) 

- Brukot (meant for university students, but has 3-6 months options for international students as well as flat sharing solutions)

- Brussels destination 

- HousingAnywhere.com 

- Brussels Business Flat 

- Immoweb

Mid/Long Term

- Facebook is a good resource. Here’s a page with different groups you may join

- Immoweb

- Immovlan 

- Appartager  (flatsharing solution)