We're nearing the end: just six more monsters! (not including the tons of animals in the back)
Wyverns are dragons and have 7 RHD by default. I wouldn't be surprised if some people end up playing an 8-RHD one, though: huge size with the corresponding ability bonuses is neat.
They're quite straightforward monsters: flight speed, six natural attacks and free Multiattack, a poison stinger that deals considerable amounts of constitution damage, improved grab, and the typical draconic immunity to sleep and paralysis. Ability scores are okay and improve with the additional HD mentioned above.
For 7-8 levels, it's a neat package, but I don't think it's worth a positive LA. +0 for now, do offer feedback.