I highly recomend reading the article at EM Practice (it's one of their free ones if you don't have access), as well as the piece at EMdocs, and why not surf Dermnet for some nice pictures to gross out your non-medico friends with.
This is based on the appearance of the lesion or rash, as outlined in the algorithm below. Some diagnoses are not that common (or present) in Australia (eg Rocky Mountain Spotted Fever and Lyme disease), but most are fairly universal.
You all know the definitions of these, of course (check the table if you have any doubts), so I've thrown in a few pictures to make sure you can recognise them.
If you see macules or papules or both, you can further differentiate them:
Petechial and Purpuric
If you see petechiae or purpura, you can also further differentiate them:
And the Others
Anyone game to name all of the conditions pictured above (without using dermnet...)?
For more information, check out the EM Practice article and the blog post, and brush up on those dermatology skills.
All of these images are hosted at Dermnetnz.org
EM Practice provide good up-to-date, literature-based summaries on topics relevant to ED physicians.