Thats what my spec is, Ret+Prot.
Only just changed to Retribution as my main, but i was Protection for along time...so if you have any questions about protection or you need a hand with talents/gear, please ask.
1 tip to start with....get lots of strength+stamina in your gear, strength is for your threat and your block, a slow main hand weapon is also good for paladins, as they dont depend on melee swing speed to generate threat like warriors, it comes from main hand weapon damage....
Broken Promise is what i use.
When you hit heroics at 80 concentrate on capping defense/hit as you wont need 540 before then really, spamming holy shield and redoubt in talents will increase your block alot.