And today, we have "What do you mean, we already did centaurs? Improvise, I like this monster concept!", the Lamia.
The lamia has well-balanced stats (+8 Str, +4 Dex, +2 Con, +2 Int, +4 Wis, +2 Cha), a lot of illusion- and enchantment-based SLAs, and a weird touch attack that drains a little bit of Wisdom. It has a 60 ft movement speed, and is a Large quadruped, so you won't be Bull-rushing it soon.
However, most of the time, it will use a regular weapon instead of the touch attack. Too weak, and 1/round. I like the SLAs, but even Charm-monster 3/day doesn't make 9 RHD interesting, even less so when the DC is Cha-based and Charisma isn't even the best mental stat of the Lamia.
Generally, the lamia is just underwhelming for what you could expect from a 9 RHD creature, but it has enough abilities to not be really unuseable. I think I will go with 6 RHD. You have charm-monster one level early compared to bards and wizards, and enough of everything to make a pretty good TWF ranger. With the full BAB, and the increase to CL, I think giving it DLA-1 is fair.
What do you think about the Lamia and this LA? The lamia is one of the most humanoid-like monsters that we covered here. Would you play it, given the choice? Next time, we have the lizardfolk, who have humanoid Hit Dice, but a much less humanoid face.