I find the zentangle pebble soo beautiful :)
And if there are no pebbles in your vicinity, try some leaves, Easter Eggs, sea shells or snail shells ;-)
Links:
Zentangle Pebble (камушек, который я вчера оставила на пляже…) (Russian)
Here at unikatissima:
Painted Leaves
Doodled Easter Eggs
Painted Sea Shells
Painted Snail Shells