Recordsets available [free resources]:

Monmouthshire Recusants 1719
[Vol VII. 1909]

Some records of the Monmouth Mission
[Vol IX. 1911]

Diocesan returns of recusants 1577 
[Vol XII. 1921]

Recusants and Priests: March 1588
[Vol   19xx]

Catholic registers of Perthir 1758-1818 

Catholic Registers of Llanarth, 1781-1838 
[Vol III. 1906] PDF format: requires Adobe Reader

Catholic Registers of Holywell, Flintshire 1698-1829
[Vol III. 1906]

Records related to Catholicism in the South Wales Marches, 17th & 18th Centuries
[Vol II. 1906]

Memorial Inscriptions
[Vol XII. 1913]

Datasets for Sale

Catholic Registers of Abergavenny, Mon, 1740-1838
£5.00 PDF Format, 137 pages.
Introduction text [on Google Documents]