Warning: these can be very absorbing. There's something about those spirals and concentric rings, drawing you in . . .
Mandala Drawing/Painting/Collage Tools:
"Mandala" at www.freegames.hu
Kaleidoscope Painter at www.permadi.com
"Mandala Maker" at GirlsGoTech.org
UPDATE: Tutorial for making mandalas from digital photos, at Earth Mandalas
And for wandering widely across the threads of the web:
Mandala Links at Zodiac Arts