Check what cover you can get with your health insurer, if you have one, such as VHI, Vivas etc. Otherwise, ACE Travel Insurance [broken link removed] has been good cheap cover in the past, but check that any cover actually gives you the amount of cover you want for specified risks, ie, read the small print and do a comparison, not just of the price.
There are many existing threads about travel insurance, what to look out for when shopping around, where to try, good deals/bad deals etc. Try searching for them.