I've booked online with all these except bmibaby.
It is also possible to take a boat + car/bus/train from, say, Britain or France. It's probably dirt cheap to take the boat plus bus/train from the UK if you buy one ticket for both from the bus/train company.
Your regular insurance may already offer some coverage. E.g., VHI offers some coverage to insured Irish citizens travelling abroad
Dublin Rail Map
Dublin Bus offers services from the airport to the city centre and beyond. Bus corridors have sped up the service on some routes.
Dublin Postal Codes: Dublin 1,2... (or D1,2..., etc.) are in the city, whereas Co. Dublin (short for County Dublin), is outside the city, strictly speaking.
has some good maps such as this Big Scale Map of Dublin (41KB) and this More detailed Map I put together (254KB)* showing the city centre in the top left and the Donnybrook Road in the bottom left that leads to Stillorgan.
Maps of Ireland MapQuest starting point.
Expedia Map site
Another map of the city centre. (281KB)*
*You may wish to save a few of the larger images to your computer (right click "Save Target/Link as") rather than opening them in your browser.