Last = coming after all others in time, space, degree, or being the only one remaining; (the one) at the end of a list, sequence, or series: ‘Our last meeting was in Rome.’ ‘I answered all the questions except the last one.’
Latest = designed/produced/published etc. more recently than any other: ‘Have you seen Toyota’s latest model?’ ‘The BBC World Service always has the latest news.’
Last but not least (Without at): ‘Last but not least, I’d like to thank our sponsors for making this evening possible.’