OpenX EU Demand Partner List
RTB House 
Quantcast
Adform 
Taboola
Remerge
Blis
Eskimi
Dynadmic
Splicky USD
Mediasmart
LiquidM
Market Resource Partners
Account Insight
EASYmedia
TapTap
Publishers Internationalé

Vendor List for Inventory to Google’s DV360
Full list of ad technology vendors can be found here.