Is what I want to pack. We are heading to Madrid Mar. 15-22 (bought tix last night, so haven't rounded out the itinerary quite yet ) and I was hoping that someone could tell me what the -warmest- thing(s) we should pack would be...

BTW, wonderful sight with lots of helpful hints/suggestions/etc. Thanks!
Emmy

A raincoat with liner should suffice in the Madrid area. For where the Action is during that week, head for Valencia: Las Fallas de San José (19 Mar) will be in full swing all along the Costa Blanca.
It can be pretty cool along the coast in mid-March, maybe enough for a light jacket. You can carry a raincoat with you on your flight to have it handy without weighing down your luggage.