Firstly, have a look here and see where you fit in
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[broken link removed]
The only way really is to get sponsorship through a job. Unfortunately, most recruiters instantly dismiss anyone who is looking for sponsorship at the CV stage, unless you can bring specific skills that they may be looking for (to be fair, there is a lot of expense and legal hassle so why would they go through this if they could employ someone locally). So unless you have in-demand skills or you know someone who would be willing to sponsor you, you may find it difficult (especially in these recessionary times). A few years ago, these visas were used by employers to get in cheap labour from India and China, but I think this has been tightened up now (insofar as there are salary checks to make sure that employers are not using these visas to replace local staff with cheap labour).
The annual visa lottery is another way, but with 9million+ applicants for 50,000 visas, it really is a lottery.
There was a report in the irish times a few weeks back about a new visa starting in the new year, but the impression I got from the article was that it would be a J1-like visa that didn't require that you were in college. Whether this has an age limit, or a 3 month time limit, I don't know (as far as I remember details were not going to be released until the new year).
Oh - just found this -
http://www.rte.ie/news/2008/0919/usvisa.html Not sure if the details were actually released fully.