We have had some crappy weather, but (so far) I have had no problem staying on the bike.
Today started dark and wet... It was pretty much still night at 7:00 when I left for work, and the weather was partly to mostly crappy - rain (but not much wind) was predicted all day.
I opted for my snow boarding helmet (warmer) and my REI rain jacket, plus some REI house-brand Scholer pants and some water-proof boots. I recently put a cheap LED head lamp on my helmet - It was only $5 at Northern Tool, and it shines,so when I make eye-contact with drivers, they get flashed. Plus, it's got a kick-ass Mad Max vibe that I am really enjoying this week.
The gear was a great combination - I was comfy and dry. I have some rain pants that I need to find - if it was any colder, I would want them, but at 45 degrees, I was just fine in this outfit (although I probably looked like some sort of clown from a Mad Max Movie to the casual observer).