Love me my Sunringle ZuZu pedals - this are BMX pedals that just rock! The bearings are sealed, the pins are adjustable. Right now they are only on my mountain bike, but I rode them on my Gunnar & LHT until I was ready to return to clipless for the road.

My feet do NOT slip off the pedals - and while I currently wear hiking shoes for mountain biking even if my foot lands on the pedal in the wrong place my foot stays on the pedal until I am at a place where I can safely adjust my foot.

I've not found non-BMX style flat pedals where my feet wouldn't slip off, that is just my personal experience.

Ergon now makes a flat pedal! Read more about it here, I've no idea how they are as far as keeping your foot on the pedal. If I hear good things about them I may consider putting them on my LHT.

MTB.com just released a review on the "thinnest BMX pedals" released by Tioga, they are also quite light and are dual-concave rather than flat. They also aren't available just yet but they looked interesting enough to mention.