Two Wheel Cool - Stretch Silicone Toe Caps
I like these better than the neoprene type, less bulky, don't soak up water, transparent , nice big toe bumper and easier to clean just wipe down or run under water.
Also they clear the cleat nicely and don't get in the way of engagement
For a sizing reference , this is the large size toe caps on size 42 (US 8.5, UK 8) Shimano SH-R320 shoes