Henry Bottomley’s Java world maps projection page dynamically redraws a map of the world based on your choice of projection and other parameters. You can also apply the projections to other layers (topographic Earth, Earth at night, Moon, Mars, Jupiter), but I was unable to get those to work on my browsers (Safari, Firefox). Via La Cartoteca and Cartography.

See previous entries: A Gallery of Map Projections; Map Projection Pages; The Peters Projection; Cartographic Projections: A Primer.