I recommend Crank Bros Egg Beaters if you can get a good deal on them, I got mine for around $50-$60 at Nashbar.com. They will work for both road & mtn. They are easy to get in and out of as they have 4 sides. They are quite simple mechanically so should be reliable.

I had tried some cheaper clip-in pedals (Nashbar brand) before I got the egg beaters but they locked up and I had to send them back. I also have used power-grips (a type of strap) which were not bad (better than toe-clips but not as good as clip-in pedals). They are easy to get out out of but slow to get into and don't feel as secure as clip-ins.

I'm really happy with the Egg Beaters and would recommend them without hesitation.