Adweek has released an industry report on top 50 interactive agencies of the world. Being a novice in the industry I had some doubts on my mind, what is actually an interactive agency? Did a quick search and found this answer. Not much elaborative though but you will get an idea [ in case you are as dumb as me, that is ;-) ]
An advertising agency, or division of an advertising agency dedicated to interactive advertising, primarily published online
From the Adweek list of the interactive agencies (affiliation)
Mysteriously the no. 40 is missing from the list.
Top 10
Euro RSCG Interaction (Havas) 1
Grey Digital Marketing (Grey Global Group)
OgilvyInteractive (WPP)
SBI.Razorfish 2
Agency.com (Omnicom) 3
Digitas
Zentropy Partners (IPG)
Tribal DDB (Omnicom)
R/GA (IPG)
Digital@JWT (WPP)
Bottom 10
Campbell-Ewald Digital (IPG)
RappDigital (Omnicom)
atmosphereBBDO (Omnicom)
Multimedia Solutions
Ten/Resource
DNA Studio
Refinery
Cadient
SimStar Internet Solutions
HSR Business to Business
Full List
You might want more current research. Here is the list for 2005:
http://www.adweek.com/aw/iq_interactive/index.jsp
The one you are pointing to is a couple years old...