Paragon
Please note that this system will be pretty much outdated after Paragon 2.0 has been released. The strategies included for faster Paragon leveling will still be valid, but the original Paragon system only applied it's level to a single character on your account (hardcore or softcore),whereas the new system will be account-wide for hardcore or softcore characters on your account.
Paragon Farming Routes
In Act 1, the popular choice for Nephalem Valor stacks is Festering Woods. 1 - 3 elite packs in the upper area, with the possibility of an event, and 2 guaranteed bosses in the mini dungeons make this a very fast zone to run. To finish off for 5 NV stacks, Cathedral 3rd floor has a guaranteed elite pack, or you could hit Leoric's Manor. Some people go straight for the Fields of Misery + Keywarden instead. Next location to hit is Weeping Hollow and possibly the Halls of Agony 2nd floor... rinse and repeat.
Act 1 areas to NOT skip ... Festering Woods, Fields of Misery, Decaying Crypt (Fields of Misery dungeon), Weeping Hollow.
In Act 2, pick a starting spot to grab some quick elites to stack yourself up. Vault of the Assassins is a good choice, as is Black Canyon Mines + Alcarnus. After you have reached 5 Nephalem Valor, you hit Oasis + Keywarden, then Desolate Sands, and then the Storm Halls dungeon ... finish off with Zoltun Kulle if you like for the drops + quest bonus. (most dungeons you will just skip over)
Act 2 areas to NOT skip ... Flooded/Ancient Cave(oasis), Forgotten Ruins(Oasis - you get ZK's head here), Vault of the Assassin (5 - 11 elites!), Storm Halls (ZK's Nexus area - good monster density), Zoltun Kulle (quest)
In Act 3, hit wp for Arreat Crater 2 ... go BACKWARD into the tower and up to the previous waypoint (should get 4 - 6 elites along the way) ... if you're still short 1 or 2 Nephalem Valor stacks, jump to the wp in Tower 1 and clear that floor (should be 1-3 there) ... then go to Stonefort and clear to end + Keywarden, then The Keeps 2 and 3, and jump to Rakkis and clear back to the waypoint on the bridge including the mini-quests you find on the way (or vice versa), finish up with The Core + Azmodan for quest. (craters used to be awesome for exp, but the Stygian Crawlers got badly nerfed on exp ... still ok for drops and gold though!)
A3 areas to NOT skip ... Keeps 2nd floor(best monster density/exp in Act 3), Frost Cavern/Ice Cave(Battlefields - good drops down there!), Rakkis(mini-quests give great exp bonus), Azmodan (quest)