The best international captain at the moment is Stephen Fleming IMO. Fleming is tactically sound and seems to be able to get more out of his team than can be expected. Ganguly is a great leader, but from what I have seen he is tactically inept with field placings and bowling changes. I have been a great fan of Waugh for his entire career, but I felt his captaincy in his last series lacked thought at times, but he is another with a great record of backing his players.
Of the retired leaders I have seen, Arjuna Ranatunga, Clive Lloyd and Allan Border stand out for different reasons. Ranatunga was able to win a world cup through innovation, a real feat. Clive Lloyd was an awesome captain of an awesome side, and Allan Border led Australia through bleak time always leading from the front (in a similar fashion to Streak at the moment, but Aussie cricket wasn't quite as bad in the early eighties as Zimbabwe).