Walmart makes a mighty thin packable rain suit. Cheap too. Some gore tex socks and some rubber gloves, and you're good to go.
I'd tend to agree with (I believe it was Moe?) who posted there is no such thing as a breathable rain suit.
I have a Frogg Togg for work, with around 100 hours in it, and sweat as much in that as a rubber rain suit.
