In contrast to diploid, haploid organisms have but one copy of each chromosome. All prokaryotes are haploid, having mostly a single naked circle of DNA rather than the complex chromosome of eukaryotes. However, there are some simple plants and fungi that are haploid, despite possesing organelles and are usually single celled. Whether diploidy and muliticellularity go together is an interesting question to which I don't know the answer.

On the other hand, just because bacteria and archaea are haploid, doesn't stop them from exchanging plasmids and generally acting like one large, distributed organism. Sharing genes (like swapping baseball cards)means that antibiotic resistance springs up everywhere and makes phylogenetics more difficult.