Einstein apparently ate meat for most of his life. However, for at least the last year of his life he did become a vegetarian. To quote directly from the International Vegetarian Union
The latest indications we have suggest that Einstein was vegetarian only for the last year or so of his life, though he appears to have supported the idea for many years before practising it himself.
"So I am living without fats, without meat, without fish, but am feeling quite well this way. It always seems to me that man was not born to be a carnivore."
This was from a letter written to Hans Muehsam, and dated March 30, 1954, which was about 1 year before Einstein died. This indicates he adopted a vegetarian diet at the end of his life. Previously, on August3, 1953 Einstein had written the following in a letter to Max Kariel, suggesting that he was still eating meat at that time:
Unfortunately more details about Einstein's diet have not been forthcoming... there is a little information 'available' from wiki.answers stating that his favorite foods were fettuccine and spaghetti, but since that site also said that Stephen Colbert eats Einstein I do not believe that it is a reasonable source.