Last tour, I had a couple of days of rain, and my breathable jacket just failed. It didn't breath once covered in water, and then the water just started creeping in, or the sweat started creeping out.
I decided then that I'd go with a Ponco. I got a really nice one:
It's waxed cotton and black - just how I like it; old world style and not at all bright.
I have some rainlegs and some gaitor style shoe covers, both of which I wore last time and worked wonderfully.
I've ridden with a poncho once, a good long while back, and I remember being struck by how much more comfortable it was. The constant stream of air underneath it seemed to take away most of the sweat. The only trouble with that one was it only had thumb straps, so the back tended to billow in any wind. This new one has a waist strap as well, which keeps it secure. I'm really looking forward to trying it out, and so, bizarrely, I'm actually hoping for rain next tour.