There will be a charity concert in Łazienki Park next weekend, namely Sunday, April 2nd. The exact spot is the Old Organgerie (Stara Pomarańczarnia w Łazienkach Królewskich).
It is said that the performers will be "Polish and Japanese pianists, both of an age and children", and that all the money will be handed over to the Japanese Embassy here in Warsaw for them to sent it to the Japanese Red Cross.
Link here: Protected content Facebook event link: Protected content
Additionally, I've stumbled upon a nice charity auction arranged by an art gallery in Seattle, the artists contributed some 50 photographs, cost of each print is 50usd and the entire money goes for two named charities - one of them I think is especially useful, "Habitat for Humanity", an organisation that builds houses in disaster striken regions.