I'd agree with the above...
Fergus Kelly's "A Guide to Early Irish Law" gives a basic introduction to the socio-legal structure of early Irish society, defining people and classes, the interaction of people and the contracat nature of early Irish law. It deals with social issues such as marriage, divorce, fosterage and children. It deals with property, inheritence and various offences. It also gives insight into the sources of the law, the law schools of the time and the later brehon septs.
Fergus Kelly's "Early Irish Farming", which is also in the DIAS early Irish Law series, is also a great book, which gives a much deeper insight into the society of the time, relying mainly on the law texts for evidence. It deals with farming, but with other social issues too. It must be remembered agricultural was at the core of the society of the time.
You have to get a hold of Fergus Kelly's books! They're a must read!
Daniel A. Binchy's works are often quoted by Kelly and in other books I've read. He's likely to be worth a look, but I've been told Kelly's books are the best sources for an introduction. I've found them very interesting, engaging and surprisingly clear, given the complexity of their subjects.
Some law texts are on CELT, as has been mentioned above. Cain Lamamna has been translated by Donnchadh O Corrain and is available from this source:
http://www.ucc.ie/celt/published/T102030/index.htmlThis is the law that pertains to marriage or unions in early Ireland. O Corrain has written a lot on early Irish society too quoting the laws, so look for any of his writings. He has a clerical background and often deals with Christianity's influence in early Irish law. The levels of influence that can be attributed to Christianity, Roman ideas and pre-Christian Irish oral traditions is a hot scholarly debate at present I've been told.
Daibhi O Croinin mentions the law tracts in some of his works on early Ireland too.
The Triads of Ireland are also worth a look. They're being discussed here:
http://livinghistory.ie/viewtopic.php?f=7&t=525 and are also up on CELT in translation.
I've never read the Life of Patrick, but it's a fairly famous hagiography alright and it's on CELT too:
http://www.ucc.ie/celt/published/T201009/index.htmlHappy reading!