Finland, Denmark, Iceland, Germany, Sweden, the Netherlands.
These countries (nor the ones GP listed) aren't socialist. Socialism is when the government owns the means of production. This means that the workers work directly for the government, and the government sells goods and services directly to consumers. Cuba is almost completely socialist, so is North Korea. Venezuela is mostly socialist, but not quite as much as those two. USSR was completely socialist, along with the warsaw pact nations.
These countries do have a few economic sectors that are socialist, such as their health care systems (i.e. the doctors work for and are paid by the government,) and in the US very few socialist systems exist but they can include things like municipal water, trash, emergency, and fire services. However when the government buys from the private sector and gives to the public, that isn't socialism, that's welfare. For example, food stamps are welfare (essentially, the government buys food and gives it to the poor, but doesn't make the food.)
And then there's communism, which in all cases has never lasted more than a few years. Although USSR identified itself as communist, it was in fact socialist.