I have now tried a few of the recommended toning shampoos: Shimmer Lights, Lush's Daddy-O, and Joico Color Endure (the one with SLS and the one without SLS). I'm here to tell you that Light Blue Shade is the best violet shampoo I've tried, both for its toning abilities and for the condition it leaves my hair.
This stuff is really potent. I don't really have to leave it on my hair for very long for a toning effect - maybe 2 minutes - which saves time and I think makes it less drying than ones you need to leave it for 5 minutes for any effect. I get constant compliments on my hair when I use this one because it leaves you with the perfect pearly ashy shade, even when you're due for an actual toner touch-up.
I'd say the only other shampoo I'd consider repurchasing (if Light Blue Shade weren't available) is Joico Color Endure violet shampoo - the one with SLS. It tones like Light Blue Shade, but its main drawback is the price.
Shimmer Lights is cheap like Light Blue Shade, but it has that notoriously bad smell. I also find Shimmer Lights leaves my hair with a coated, waxy texture.
ETA: Ugh, why. Of course after I wrote this review, I ran out of the shampoo and went and bought a new bottle. The design of the package and label had changed and - guess what - apparently the formula has been changed as well, and this shampoo tones nowhere near as well as it did before. It's not really worth it anymore. Guess I'll be shelling out for Joico Color Endure until I find a cheaper alternative that's as effective at knocking out warm tones.