I have a tiny jar of Vegemite in my house, which is the yeast extract used largely in Oceania. Marmite is the closest thing commonly found in Europe, and more specifically Britain. I have tried it a few times, but I don't like it all that much. I know that if I had a few weeks of it, it could come to be one of my favourite spreads, but it is made by Kraft, and I boycott Kraft.
Other brands of yeast extract include Marmite and Promite.