What albums (or songs, if you've simply been downloading) have you listened to by these guys? Their first two albums have a different vocalist then their two newer ones, and their sound has changed significantly enough that I might be able to introduce you to some similar bands in either of their styles.
Old albums =
Killswitch Engage and
Alive or Just Breathing and are more thrash/metalcore.
If you liked these albums, may I suggest: As I Lay Dying, God Forbid, Mastodon, Shadows Fall, Lamb of God
New Albums =
The End of Heartache and
As Daylight Dies and are more melodic metalcore.
If you liked these albums, may I suggest: Children of Bodom, In Flames (esp. the newer albums
Soundtrack to Your Escape and
Come Clarity), Port Amoral, Avenged Sevenfold and Trivium.
If you liked either of these 'eras' for the band, you'd also probably like DevilDriver and Unearth. Also, pick up a copy of Roadrunner United: the All-Star Sessions. Read
here for more details. It has an excellent variety of metal sub-genres on it, and is a a fantastic listen that you'll keep going back to - and many of the band I mentioned (including the newer Killswitch Engage vocalist) are featured on this album.
cheers,
--N