I'd avoid Nature Diet at the moment, as they seem to be having some quality issues.
Lily's Kitchen wet good is good stuff.
I'm using Forthglade in my dogs' kongs at the moment and that seems to be going down well as a change from their usual sardines in tomato sauce. They're having the chicken and tripe mix, which is good for keeping weight on over the winter and also kind to the stomach (assuming your dog is ok with chicken).
I'm buying mine from Vet UK - cheaper than PAH and generally 24/48 hour delivery at most.
When our old boy was in late stage heart failure he also went off dry food and he did really well on the Wainwrights salmon and potato. It used to only come in tins but I've had a look on their website and I think it's available in trays instead now.
Zooplus do some really good European brands of wet food in some really interesting flavours. We use Rocco Classic at the moment and the dogs go mad for it, especially any of the varieties with heart in.