Oh boy. DH compliant Snape. This is a complex issue for me, and one I don't like to think much about.
I thin he probably had motivations other than Lily, but I think those same motivations are tied in to Lily, somehow.
For example, I think that he felt like helping Harry was serving Lily, and by serving Lily then he redeemed his own soul. I think it is quite telling that Dumbledore asks Snape "how many people have you watched die", and not "how many people have you killed", because I think that demonstrates that Snape's soul was as whole as it could ever be under the circumstances of growing up in a home where your parents don't love you and care about you, and where you have no friends save one, who really doesn't value you as much as you value them. It seemed like Severus was "convenient" for Lily, whereas it seemed like Lily was EVERYTHING to Severus. She was certainly his only reference for normality and affection.
I think Severus' anger in the memories shows this. He's angry at being misled, angry at Harry being "raised like a pig for slaughter," because in that slaughter, it seems like Snape loses the only opportunity he has to redeem himself for his past crimes, and specifically redeem himself for the death of Lily.
It's like, she died, and if Harry dies and her sacrifice was in vain, and Severus could have prevented that, not only did she die because of him, but he failed to prevent it from being a useless death.
So in short, yes, I think Snape had other motivations, specifically his own redemption, but I think that redemption was very intimately connected to Lily.