If you don't need the power of a 550EX for every strobe in a multiple strobe setup, and you're addicted to Canon's wireless flash triggering system, the Speedlite 420EX, announced yesterday, may be for you.
420EX front and rear views
It has the same E-TTL flash metering capability as the 380EX it replaces, but adds the ability to serve as a remote flash when triggered by either the 550EX or ST-E2 transmitter. Note that it can act only as a slave unit, not a master unit; you'll still need a 550EX or ST-E2 to serve as the master unit in a wireless configuration.
It should sell for under US$300 when it ships in October.