I have been using rio power flex leaders and tippet for all of my fly fishing. Recently I have noticed that they fray easily and don't straighten very well, making my dry flies look pretty unnatural (a few inches from the fly, it gets crinkled from knot tying). Does anyone know of any better product? I've heard the build your own leader suggestion but I'm not sure if I'm comfortable with so many knots

I've made leaders from leader material (if you try this buy the stiff stuff and do a search to find some good sites on  lengths of each pound test and the best knots) and if done right they really do turn over better, especially on bigger flies.  But for smaller dry flies I think the knotless Rios and other name brands are very good.  The secret I've found on straightening them is heat.  I have found that just using my hands is better than a leader straightener.  You need to really pull the material hard through your hands, trying to generate heat as you pull.  Practice it and you'll probably find the same thing I did.  

 

The crinkling right at the knot will be worse for some knots than it is for others.  The ones that require a long pull through will crinkle more.  And it's especially hard to straighten the last inch or two, so you may have to just cut that off with each new fly to minimize that length of crinkled line.

 

http://www.offthehookflyfishing.com/blog/lefty-krehs-no-slip-loop-knot

 

This loop knot looks like it will tie well without much crinkling.

If you don't want a loop knot, tie the knot with little or no loop diameter by sliding the "circle" down almost to the eye of the hook.