Max Cowan shares some of his memories of Penrith on his website 365 Short Memories.
Penrith Library has a website called Penrith City Local History.
A more contemporary blog is Living next door to Sydney
The Nepean District Historical Society looks at Penrith from its earliest days to the present.
Facebook groups
There are some interesting Facebook groups too.
Penrith High School when it was truly selective
Memories of Penrith and surrounding suburbs
Penrith and the Nepean Valley History and Memories