I know, I know... I keep mentioning this, but it's my new fave summer hair look. I love it! It's so different, and I never see anyone else with it (which is why I like it!).
I used Wella's Color Charm hair glaze in 4N on the top 1/3 of my hair... (don't worry
about it leaving a noticeable "line" between colors... it evens itself out. I went ahead and left the bottom 2/3 of my hair the color it was already (carmel brown)... or you could buy some hair bleach from a beauty store, and leave on ends for however long until you reach the color you like. (be careful with the bleach though! It can be tricky.)
The celebrity that inspired me was, of course, the lovely Megan Fox. Some people think it just looks like a bad "grown out roots" look, but I think it's natural and summer-y looking.
A couple of other celebrity ombe hair looks that I love...