I get h4 euro bulbs from a place in Britain -- powerbulbs.co.uk. They can ship the two most popular +50 bulbs, Osram Silverstar and Philips Vision Plus, for about $36 per pair shipped. Both bulbs will deliver noticeably more (not "bluer") light than standard 55w60 h4 bulbs, IME, and have proven reasonably durable in my cars. I have a pair of each that have lasted through about 15K-20K miles of night driving.

Powerbulbs apparently has a new high-output product from Philips, but I can't comment on that from firsthand experience.