It's perhaps a little tacky to put your own studio in a list like this, but it felt weird to not get us in here. (For those of you unfamiliar with smashLAB, we're the people behind MakeFive.)
http://www.smashlab.com

These guys showed up on my radar as a result of all of their posts on www.undrln.com. Needless to say, I've seen a lot of sites for interactive groups. The thing I like about Teehan+Lax is the focus on usability and avoidance of "flashy stuff", which is all too prevalent in the agency world.
http://www.teehanlax.com/

They have been best in world for many years now.
http://www.f-i.com

I don't know much about Modernista, but I like how they approach their website: ultimately it's a mash-up of other technologies. As such, their portfolio is shown in flickr and their about us section is from wikipedia. Very neat approach!
http://www.modernista.com

Red Interactive
http://www.ff0000.com/

I've been a fan of this studio since they were called Epoxy. Their aesthetic is completely different from mine, which perhaps is why I like it so much. They do brave things and seem to play a lot. I like that.
http://www.amencreation.com/

http://www.collemcvoy.com/

Area 17's site feels pretty out of date and the type is microscopic; nevertheless, I always think they pull together rather neat work.
http://www.area17.com/

Another top for 10+ years :)
http://www.2advanced.com

Award winning web design for more then 10 years.
http://www.MindSmack.com

Blitz is old school and does truly awesome work.
http://www.blitzds.com

EYE4U has the best original website on the internet for interactive. I remember in 1997 when I saw how cool it was. Amazing :) FLASH 3 WOOT
http://www.eye4u.com