Designing and implementing a payment processor is no small task. There's a tremendous amount of work that goes into making absolutely sure that everything is secure and safe to use for the end-user.

That being said, CryptoAve is currently in development and will provide payment processing for LTC (along with BTC, DGC, SRC and ARG). It's still several weeks away from launch, though.

https://bitcointalk.org/index.php?topic=277241.0