Virtually all variegated plants on the market are found as chance mutations in a garden or nursery -- so I always keep my eye out for leaves that look different on the off chance that I'll find something exciting.
This past weekend I found not one but TWO variegated plants in my yard. Both weeds, sadly, but still, cool all the same.
This variegated queen anne's lace (Daucus carota) shown here against its plain green neighbors, is actually quite pretty, I think. Sadly, it is a biennial, so the only way to propagate it would be by seed, and this type of variegation is virtually certain not to come true from seed.
This narrow leaf plantain (Plantago lanceolata) has variegation that looks unstable -- half the leaves are variegated, half aren't, but I'm hopeful it will stabilize with white leaf margins. Plantain is a perennial, so propagation would be no problem, and really, it looks more like a rare and expensive hosta than a weed! Of course, it will still seed around like a weed, and have plain, green children... but still. Pretty cool. Now if only the non-weed residents of my yard would follow their example and throw variegated sports as well I would be REALLY excited.