I like to do a peanut butter and Vegemite sandwich, from time to time - the creaminess of the peanut butter helps bring out some of the more complex flavours within it.
Avocado and/or cream cheese also work to augment the flavour in a similar way - so basically anything with a good dose of fat should do the trick!
We also had a limited edition Cadbury chocolate block with Vegemite here a few years back - I think the general consensus was that it was loathed, but I dug it.