The Houdini packs down in its integral pocket to just slightly larger than a male's clenched fist - thus it always sits in my bag, ready if needed.
I'll have to see if I can get one on sale.
Almost as compact, and somewhat more sturdy, is the Marmot PreCip jacket. I have seen those on sale at Sierra Trading Post for around $60. Hard to get anything decent any cheaper than that. The PreCip has worked very well for me - I wear it regularly when cycling in wet weather.