Remember that unlike just about everything else in the MM, the CR for Dragons assumes that the party knows that they're facing a dragon, and have prepared for it.
Red Dragons are incredibly arrogant and greedy SOBs that take victory for granted. Since any adventuring party actually capable of taking one on would shield itself against fire, and fire breath tends to ruin treasure, it's pretty reasonable for the dragon to not bother with its breath weapon. Fire breath is for emergencies and when it's clear that nothing of value would be lost to it.
If you want to be an ass, put Shield, Mage Armor, and Shield of Faith in it's spell list. A simple dispel magic would clear all of that away, but the expression on the fighter's face when he realizes that he has to hit AC 39 or so should make it worth it. On that note, the dragon should eat the spell casters first, since they're far more dangerous to it than the fighters are.
Trolls could be neat minions; they'd be utterly terrified of the Red, since it's one of the few things they've ever met that could kill them for good. A cluster of small fire elementals could also be interesting, since they can't possibly hurt the dragon, and the dragon doesn't have to worry about killing them through collatarel damage.
Mountains are the classic lairs for Reds; it should have multiple exit and entry points, at least some of which are only practically accessable through flight.
