I have rethurned!
The Reth Dekala are one of ToB's more unique monsters (not like there's a lot of competition, but still). As CR 4 outsiders with 5 RHD, they're the weakest of the book's three creatures, but still plenty stronger than many of the things that've been reviewed so far.
Reth Dekala have the [Evil] and [Lawful] subtypes, enjoy +2 natural armor, and are medium-sized. Their ability scores are considerably above average.
Furthermore, the creatures have resist 15 to both acid and fire; both fairly common damage types, and benefit from a continuous Air Walk effect. It's not true flight, but it's the next best thing, and as the book notes effectively translates to a +1 to-hit in every battle. 50% fortification is icing.
Finally, there's Vilefire Aura (decent debuff, though annoying for your allies), and Vilefire Blast (beats the average warblade's backup longbow, but that's about it), and a number of martial maneuvers. The ones known can't be changed, but they're decent picks.
Interestingly, a reth dekala who takes levels in any of the three martial adept classes can effectively add their RHD to their class level when determining available maneuvers and initiator level. For crusaders and swordsages, this means a slight decrease in maneuvers known, but for warblades it's superior to a non-LAd race in almost every way (unless you really wanted Improved Uncanny Dodge, I guess).
With this in mind, I think reth dekala deserve at least +1 LA, and possibly +2. For now I'll rate them at +1, considering their lack of maneuver choices, as well as the reduced appeal of outsider HD when the balance points get the closest thing to it.
This assumes a tier 3 balance point.