What Line

What type of line do you guys recommend for casting lures with an ultralight spinning reel?

Thanks

I am assuming that your rod is ultralight as well. If so, I would not go above 6lb. test. I use 4lb. on my ultralight rod.
If your rod has a line recommendation on it, I would go with a line about in the middle of that range. You want the line to be the weak link. You want it to break before the rod does. Line is much cheaper than rods.
As for type, there are two schools of thought. Some say that mono's transparency gives it an edge, while others feel that braids thinner diameter and better sensitivity make up for it's lack of transparency. But there are some special considerations you need to be aware of before using braid.
I fish with both (though not for trout) and really don't notice a great deal of difference as far as catching fish. The braid I use is moss green 10lb. Spiderwire. For most of the lakes around here it works well, as the water isn't very clear.
If the water you fish in is very clear, moving water then mono might be better.

i prefer trilene xl for all my line line applications. i know the braids are more sensitive, but it is hard for this old dog to move beyond tradition.

I posted something about this in your other thread - didn't look down and see this one. 4 lb. test mono. on an ultralight rod unless you are going after monster brown trout. Then I would probably use a 6 or 8 lb. clear line.