Warm browns, copper, gold are good to enhance brown eyes. Personally (although "experts" won't agree with this), I like a touch of blue on blue eyes. It just makes you look like you have huge blue eyes! IIWY, I'd line my top lashes with a medium brown eyeshadow and then use a blue eyeshadow (about the blue of your eyes) to line the bottom lashes. Here are some other tips:
A) Cat's Eye - Apply a thin line of e/s to your upper lashes only, using an angled brush (damp or dry). Flick the line up at the outer corners. You could use either color for the Cat's Eye.
B) Apply a sparkly gold-ish eyeshadow to the inner 2/3 of your upper lids. Then smudge a warm brown into the outer corner.
C) Whatever style you choose, you can always apply a white or fleshtoned eyeliner pencil to your bottom waterline too. That really brightens up the eyes.