Micromedex/Posindex is a database of toxicological information which is available through the Clinicians Health Channel to subscribers (all Victorian public hospitals have ISP based login, Victorian public hospital employees can register for off-site access for free). It contains an extraordinary amount of information but can be a little unweildy. Type the name of a drug or substance and then click on "View Summary Document". It is particularly helpful for identifying the active ingredients in bizzare househould chemicals and for finding the lowest dose of a drug at which anyone has had significant symptoms (undr "Range of Toxicity" at the end of each summary monograph.
Wikitox is a collaborative effort by a group of interested toxicologists from around the world. There is a significant presence from Australia. It has a more friendly layout than Poisindex but as a wiki it is open to some degree of non-expert contribution and relies upon editorial review and some degree of crowd wisdom to maintain its standard. It is a really excellent site for learning from. The team at wikitox also run a 2 year, 4 semester, distance education course in an open-university style which can be found through the site.