I've been debating on whether or not I should invest in a decent one-piece, all-season, waterproof textile riding suit, or just gear up per usual and don a dedicated rain suit as necessary.
I like the idea of not having to stop to change into rain gear, but I also like the comfort and convenience (think: restrooms) of what I already have. This is hard to beat:
Tour Master Elite II One Piece Rain Suit
Yellow and red have been discounted to $39.99. Sure, it looks like a senior citizen's jogging suit, but it's high-viz and it has cool features for the price. Packs small and looks easy to pull on.