A website that I have used frequently when checking information about my convict ancestors is Free settler or felon.
The section I have been using primarily is the Convict Ships Index which provides detailed information (when available) about each ship bringing convicts to Australia as well as the journey. Sections from correspondence from officers or from ship logs is often used to portray the conditions faced by those on the ship.
The site specialises on the early colonisation of the Hunter Valley region in New South Wales and is an invaluable resource with those with ancestors who settled in this region including, Newcastle, Mailtland and Port Macquarie.
However, as well as the Convict Ships Index, there are sections of the website providing general information such as a section of the Parramatta Women's Prison where many of the convicts were initially sent and a section on Colonial Events which can be searched by year.