The correct spelling is ridiculous, derived from the same root as ridicule – few people write redicule. I’ve seen this abomination in spelling become very common online recently. Maybe you have friends who pronounce it reee-diculous, but that doesn’t change the spelling. I never cease to be amazed at how many college educated people I know with not a prayer in the world of spelling simple, common words. Don’t even ask about writing coherent sentences. How do we turn out so many highly-educated people with so little ability to use our primary language, much less learn a second language? It’s so common that it’s ridiculous.