The Irish Genealogical Research Society (IGRS): http://igrsoc.org is a well-respected organization based in London, with an Irish branch. It was founded in 1936. This is an important society which has helped to preserve, and make available privately held Irish records. Membership is open to anyone interested in Irish family history.
The IGRS was founded due to the destruction of the Public Record Office in 1922. The society set a goal to locate and preserve printed and manuscripts dating prior to that date, which includes wills, genealogies and Church of Ireland registers to name a few. The best use of their holdings for the family historian is when the family lineage has already been traced back to the mid-1800s.
The IGRS has created the largest private library of Irish genealogical material in Britain. They publish the widely acclaimed journal The Irish Genealogistonce a year since 1937. They also publish a bi-annual newsletter. The society has launched a monthly bulletin about Irish genealogy. Most major libraries with Irish collections will have the journal. Issue from 1937-1993 are now available on CD from Eneclann: www.eneclann.ie
The IGRS library is staffed by volunteers, and they cannot undertake private research. The benefits of society membership is access to the library and online resources. A list of the major manuscript collections housed at the IGRS library can be found on the society website.
If you are well-versed in Irish genealogy, you probably know about the IGRS. If you are a new to research, then I would suggest you find copies of their journal for study, explore their website, and see at what stage of your research, you may be ready for membership. Their goals for Irish research are certainly the same goals we all have regardless of what country we live.