I am a makeup artist at ULTA, and I have found that Urban Decay is the best eyeshadow primer and Benefit Porefessional (not a typo) is one of the best foundation primers.  Howver, Stila also makes an excellent primer, as does Smashbox.  Smashbox has several different ones to do different things, like getting rid of red, making skin tone even.  I have also tried an unusual primer - L'Oreal Souffle makeup.  I put that on first, and it really covers wrinkles and gives a good blank canvas for the Too Faced Foundation on top.  It does not feel like I am wearing too much makeup because the Souffle is light and feels like a primer.  I alternate among Souffle, Porefessional and Stila.  (depending on my mood.)  Too Faced just released a wonderful new liquid foundation that makes your face glow.  Hope this all helps.

I like Urban Decay shadow primer too and I was sort of recently converted to the wonders of foundation primer too!

Because it made my eye makeup last longer, I started wearing primer under my foundation to make it last longer (plus it goes on WAY smoother). I really like the one by Pur Minerals. I got it from www.ebeauty.ca and got it in green. It helps fight red skin which is awesome because it does double duty as a primer, more bang for your buck! They have it in a dark spot corrector and under eye circle corrector too, so you could really get specific and target your other skin needs while you're at it.

Good luck!

I just recently started using foundation primer and love the smooth look it seems to give me... 

I use Smashbox for my face (though I've tried Mercier, Geller and a few others).  It fills in pores and provides a smooth surface for the foundation.  I love Urban Decay lid primers but have also found that a bit of any concealer tapped on lightly with a finger works just as well.  I've found that the lid primer keeps the shadow on longer and the color looks better too.

So, though some people say don't bother with primer, with my dryer skin, primer works for me.  Also, I would think if you tend to oilier lids, shadow primers would work well also.

I have only used MOTIVES by Loren Ridinger Perfecting Face Primer. It makes my face feel and look flawless.

I would like to try Urban Decay's shadow primer, though.