Here is a list of hand picked CSS corners that you can use in your design.
Text Revel on Hover: Corner Triangle Slide Overlay
Dev: David Leininger
Demo: Pure CSS corner ribbon
Dev: Naoya
CSS Corner Shape Mixin
Dev: Ryan Dunn
CSS Only Corner Borders
Dev: Vian Esterhuizen
CSS corner-cut
Dev: Mohammed Fahsi
CSS corner curl
Dev: Jim Warwick
Corner Shadow
Dev: Sean McCaffery
Clip border CSS
Dev: Scott Kellum
CSS Corner Fold
Dev: Kevin Kipp
css corner notches with box-shadow
Dev: Jason Kuhn
Paper with sellotaped corners
Dev: Suzanne Aitchison
Tucked Corners (1 element, flexible method)
Dev: Ana Tudor
Fancy Corners with Gradients in CSS Masks
Dev: yoksel
Image w/ Corner Frame
Dev: James
Corner Border Link
Dev: Vian Esterhuizen
Folded corner
Dev: Steve
Box corners animation
Dev: Lukáš Werner
Card with rounded corners
Dev: Jaroslaw Hubert
Random Rounded Corner + Blend Mode
Dev: Mana
Infinity glowline CSS corners box / buttons
Dev: Sabin Tudor
Cutting Corners with CSS
Dev: Martin Duran
Tucked Corners
Dev: chorn99
Dynamic Sharp Corners
Dev: Wixel
Bubble corner effect
Dev: Ricard
Pixel corners
Dev: C4rin3