[titan9]

It kinda depends on whether you want stuff from the Christian or Secular genre. For good Christian bands like Creed and Alter Bridge, I'd recommend the following:

Day of Fire(features Joshua Brown, who was the lead singer for Full Devil Jacket, a band that toured with Creed)
Kutless(has some hard rockin' songs that are similar to Creed)
Seventh Day Slumber(again, their hard rockin' songs are similar to Creed)
Pillar(not so much like Creed, but an awesome hard rock band)
Skillet(an awesome hard rock band)

Some good secular bands:
Virgos Merlot(just started getting into these guys. They released one album in 1999 and I believe they toured with Creed. They featured Brett Hestla on vocals, who was Creed's touring bassist and is now the lead man for Dark New Day)
Mayfield Four(not quite like Creed or AB....really, I don't think I can compare them to any one band in particular, they're that unique and different. This band of course featured Myles Kennedy on vocals and they put out two really awesome albums)
12 Stones(some similarities to Creed, but most are quite subtle. The vocalist is an awesome screamer and the lyrics, particularly on the first album, are quite good)

Other than those bands I mentioned, I second Lithium's suggestions.