M.L.
When I do highlights, I keep them in the same tonal family. They will both be consisted of bleach, but one will have a hi-lift color added to it.
That way, the highlights are in a similar family, so you aren't ending up with cool contrasting against warmth.
There is a ashy tone to parts of your hair, but I'm guessing that is the flash. If it's the flash, a warm golden highlight no higher than a level 10 would look lovely, with another highlight around a level 9.
I tend to agree that you could pull off some lovely lo-lights in an almost warm, autumn red color, like a soft, coppery ginger.
One thing to avoid, is getting blonde highlights too fine. It will often tend to make brown hair like yours almost appear graying, especially if they are cooler in color. I don't mean to get super chunky pieces, but a few blondes back to back with lo-lights in between every two or so foils, then every other foil, then again two back to back blondes...
If you get 2 hi-lights, 2 lo-lights plus your natural hair, you will have 5 colors. I would stick with 2 hi-lights, 1 lo-lights and a nice, soft, glaze like Sebastian colorshines to go on top to bring out the richness in your natural color as well as the highlights. Glazes are non-damaging and they actually protect the hair and make amazing shine. The color can be adjusted to clear, to a rich honey wheat that looks lovely on pretty much any color.
ANYWAYS!!!:
These are some colors that *I* think would look great on you:
http://www.flickr.com/photos/number9salon/3890722331/ (but I would have more of your brown hair showing and a few blond pieces that are brighter/blonder)
http://www.gallery.becomegorgeous.com/hair_highlights_ide...
http://www.becomegorgeous.com/img/user/d/1/1/4/barbipixi/...