Generally several books come to mind;
My three 'korans' are;
R. Lobel,
Coincraft's Standard Catalogue of English & UK Coins; 2000 (London, 1999) [Third Ed.]
J. J. North,
English Hammered Coinage; Vol. 1; c.600-1272 & Vol. 2; 1272-1662 (London, 2000) [Third ed.]
E. Hawkins,
The Silver Coins of England (London, 1841) [First ed.]
For historical background knowledge on the periods, online i like Wikipedia. As for the Catholic Encyclopaedia yes i have made use of this in the past. What i really like about that site is the agenda and bias is obvious, which is what you want from reference works. Best to know the angle they are coming from so you can realise how it's been shaded. Easier to find an obviously biased article than it is to have to cross reference more subtle reference works to weed out opinion from fact. But that's just my biased opinion.

If it's an English coin though i tend to prefer digging out any number of books for general background info. I have an incomplete run of the Oxford history of England volumes. I think there were 14 volume in all, i have three...

Two that have been used for sure are;
F. Stenton,
Anglo-Saxon England c.550-1087 (Oxford, 2001) [originally published in 1943]
A. L. Poole,
Domesday Book to Magna Carta 1087-1216 (Oxford, 1958) [Originally published in 1951]
I also have a copy of some primary sources namely the Anglo-Saxon chronicles which record the history of England from the first century AD to 1154 and were written in middle English, these are useful for such things as the Danegeld payments. It also gives a sublime feel for contemporary events and how they were percieved at the time. I also have a copy of Henry of Huntingdon's Chronicles which were written during the 12th century and cover the time period 1000-1154.
I also have some scanty photocopies here and there of other harder to acquire primary documentation (incomplete), namely parts of Matthew of Paris's account of English history and The Historia Rerum Anglicarum of William of Newburgh. Both of which are written in Latin and require some concentration with a dictionary... mostly a dictionary. Although i think the following phrase was quite obvious, blunt and amusing; "Veneribili Turstino defuncto" (entry for 1143) Thurstan Archbishop of York died.
The Domesday book is the next one on my to get list.
Although i have some articles of Æthelredian Coinage that i've yet to read thoroughly. That were originally lectures at the Millenary Conference in 1978 to celebrate the 1000th anniversary of Æthelred II's succession.
So i'm not short of sources.
Browsing the internet i've also caught the sight of two new books scheduelled for release sometime this month on the 1135-1154 period. So i guess i'll be trying to get hold of those too. Not to mention that Sharon Penman's novel i'm reading; "When Christ and his Saint's slept" which is the early life of Henry II of England told with remarkable accuracy, and this is set in the 1135-54 period also. I'm only borrowing this though!
Sometimes i wonder if i'm a bigger book collector than a coin collector!