As Yesnomu said, anyone who can get Fire Resistance 10[...]
Such as any tiefling character - a level 20 tiefling has 15 fire res without boosting it with feats or PP:s (can't be bothered to look up any). Not that i mind that specific example - racial abilities should matter.
Edit: More
Boat Admin said:
Thinks: it is an epic foe. How easy/hard is it to get resist 10 fire at epic levels?
Firesoul Genasi get resist 10 fire at level 11 (and resist 15 fire at L21). Still racial, no biggie.
Dragonsoul sorcerers can choose fire resistance and will have 10 at level 11. Wild magic sorcerers roll a d10 for their resistance after an extended rest, and fire is one of the possible results.
Level 14 Black Iron Armor (scale/plate) gives resist 10 fire.
Level 14 Flamedrinker Armor (plate) gives resist 10 fire, and can give allies within range 5 resist 20 fire for a turn.
L19 Cloak of Survival, resist 10 fire.
(Items from PHB1 only, not slogging through the rest.)
The Radiant One (Epic Destiny) gains resist 10+level to "radiant fire" at level 21. Bit late, maybe.
The Prince Of Hell (Epic Destiny too) gains resist 20+half level at L21. Same problem.
Paragon Path resistances seem to be more temporary, but a Wildfire Genasi can share its fire resistance with any ally within 2 squares. (Mang, that's nuts - not just when fighting Remorhazes.)
Not checking powers, probably just temporary fire resist anyway. I don't see much of a problem, though. Two strongly fire-themed races and three sets of equipment (heavy armor or a cloak) let you ignore the Remorhaz' aura. Meh.