Come on over to here for some more ireland-centric discussion.
For that sort of distance defo go for a racer or flat-bar racer, you can use any speed advantage you can get over that distance. Contrary to popular belief it only rains about 10% of the time in Ireland - which means that if you commute both ways each day you will get wet on average one commute a week.
Where are you cycling to/from? If you're coming into Dublin you will really need to pick your route carefully, as some of them have terrible cycle-tracks, terrible drivers - commuting in Dublin is really an adventure. Stupid people are allowed to drive cars. It boggles the mind. But as I said come on over to boards and there's a wealth of info there, and we can give you more specific deets.
Would it be an option to drive halfway in for a bit and dump the car before jumping on the bike for a 30km commute?