Bacteria are some of the best examples of prokaryotic organisms. These organisms do not have a membrane-bound nucleus and lack the well-distinguished cell features found in eukaryotes.
Specific examples of prokaryotic organisms include the Escherichia coli bacterium and the Streptococcus bacterium. These are more recognizable as E. coli, a bacteria often found in meat, and the bacteria that causes strep throat.
There is an entire kingdom devoted to prokaryotes, named Archaebacteria. These prokaryotes are ancient forms of bacteria and are notable for living in extreme conditions, such as geothermally active pools and extremely acidic waters. They are considered to be the oldest living organisms on the Earth.