Delirious and Hillsong ( especially United but I also like the Darlene Zschech led group ) are tremendous worship bands. Delirious live are especially good, check out Live at Walnut Creek if you haven't already ).
I also like Matt Redman , Tim Hughes and Chris Tomlin. Tims last album, Holding Nothing Back was amazing.
My real no 1 favourite Christian band however are Casting Crowns - 3 albums to their name, and the latest "The Alter and the Door" is up to their usual high standard - they are a band who devote much of their time to touring their material and spreading Gods Word through their inspirational music, but also still are actively involved in youth ministry. Check out "Who Am I " as the perfect introduction to this band.
Another band I enjoy are Leeland - I saw them on the God Channel performing at Frenzy Edinburgh last year and their debut album Sound of Melodies is a strong debut album from a young but talented Christian.