I really like the Cambro polycarbonate storage boxes. I may even build my hatchling/grow-up rack around one of their products. They're expensive, but quite durable. The only issue with them is that if they do scratch the polycarbonate is not as easy as acrylic to buff out.
Kingsnake has no issue with posting sites of suppliers, etc. so you can view/order Cambro polycarbonate tubs here.
BTW, if the clarity is for viewing and enjoyment of your animals, then I'd recommend splurging for the 9" tall products. It really does make it seem more like a small terrarium that way and does not "cramp" the view.
But if it's just for checking for eggs or uneaten food then the 6" is fine.
Reptiletubs.com also carries some plastic boxes that are quite clear. They are more like regular plastic boxes, just more clear. You can read more about them on their site or go directly to Iris' online PDF catalog.
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Current snakes:
0.2 Gonyosoma oxycephala - (Silver/Yellow)
3.3 Gonyosoma oxycephala - (Green)
2.1 Gonyosoma janseni - (Black)
3.3 Gonyosoma janseni - (Black & Tan)