http://www.castnetworld.com/bettscastnets.html

I use Betts Old-Salt Monos at 8 foot in size. Strong, but if push comes to shove you can most times force pull it off a snag.

Not too expensive, and pretty tough and pretty good quality.

To keep it limber, grab a 5 gallon bucket, drop net in fill with water, and add a cup of fabric softner. Helps make the net easier to thro, easier to untangle, and it gets the "shad" stench out of it.