Eli Young Band - Even if it breaks your heart, if you like country.
Boiler - Limp Bizkit. Old-ish school stuff
Decaf- Supafreak, Pinky Boy, Top Chef, Money man, Phone Number, Hard in the paint...And well...Basically anything else (I still have a sealed box, ftl)
As for rock, if you want something different, it may not hit "the best", but I think these sound pretty good in my car:
Im sure alot of this has been mentioned but eh-
Rise Against - Savior
Slipknot - Vermilion
Another Bottle Down - Asking Alexandria
Killswitch Engage - End of Heartache, My Curse
Manson - Dope Show
Nickelback has alot of stuff that sounds good (even though its nickelback)
The Offspring - You're Gona Go Far Kid, Hit That
Theory of a Deadman - Hurricane
Tool..Most anything
All That Remains - Two Weeks, This Calling (fuggin fast kick)
Alexisonfire - Pulmonary Archery, This could Be Anywhere in the World
Avenged Sevenfold, Bobaflex, Breaking Benjamin, The list goes on and on. But theres a good start for people looking for new stuff!