I love my punk/hardcore to be quite melodic, preferably with great vocal harmonies too, so I love Bad Religion.

My favourite album is Against the Grain, but I'm not familiar with their post-Stranger than fiction output.

I'd be interested in checking out their latest three or four albums.

Any recommendations?

For starters if you haven't heard anything after "Grain" check out "Stranger Than Fiction" and "Gray Race" those are amazing.

From the last 4 records...i'd recomend "The Process of Belief" but check out "Gray Race" if you really want to hear some melodic stuff.

As I said, I already own (and quite like) Stranger than fiction.

I also have No control, against the grain, generator, recipe for hate.

I'll check out Gray race and The process of belief, thanks for your reply.

empire strikes first is really good as well. but, in my mind, Bad Religion can do no wrong

Definitely check out their latest effort: New Maps of Hell. The band has taken a new direction for sure, it's got a much darker feel, it's punk, it's well crafted, high caliber grittiness.
I must add that I love Against the Grain immensely; Quality or Quantity is my mantra.