Dave,
Here's my list of the most difficult. I'd be interested in hearing from anyone that has one in their collection, or even better, for sale.

tan-sunburst
brown-card pips, satellite
lt blue-windmill
drk blue-four square, hexstar, three diamond, windmill
orange-dbl anchor
green-fireworks, four sqr, three diamond
pink-pin wheel, snowflake, windmill