Hakuhodo S142 and S146 (from the S100 series) are perhaps the best crease brushes I've tried, at least for working with finely-milled silky soft eye shadows. Both are made of blue squirrel hair and sport the vermilion handle of Hakuhodo's top-of-the-line series. They're dreamily soft (too soft to pick product that has a somewhat hard texture), springy and just fluffy enough for blending.
I can't say enough about the softness. These are the brushes I never hesitate using even when my face feels raw and painful after an allergy attack. They are dense enough to use with the most delicate eye shadow textures- the ones that give you a hard time if you go at them with a stiffer brush and leave fall out all over the place. Not with these Hakuhoso brushes, though. The S142 and S146 don't disturb the surface of the product too much and only pick up what you need. Then they deposit the color on the lid or crease and blend it perfectly.
Both the S142 and S146 are narrow and pointed, making them ideal for crease work. You can use the tip and then the side in your favorite blending technique.
Hakuhodo S142 is the larger of the two. It's closest in size and shape to Paula Dorf's Sheer Crease brush, only pointier and softer. The S146 is a refined, narrow version that would work especially well for those who have smaller lids and creases. I often use it to blend and diffuse powder shadow over an eyeliner.
Bottom Line: it doesn't get much better than this.
Hakuhodo S142 ($27) and S146 ($26) Eye Shadow Brushes are available from hakuhodousa.com. They ship internationally.