Far and away the best gallery plugin of its type out there... Whenever I start a new project, its the first thing I get my clients to go and buy - I won't build sites without it any more :)
I've wasted too many hours tweaking WP post or gallery outputs into something slick, stylish and responsive. And pulled out too much hair trying to battle against the various implementations of Masonry, lightboxes and the like. Justified Image Grid just works as you'd expect it to, and the customisation options mean you can pull it into pretty much any shape you like without breaking a sweat.
Combine this with the range of source options available (including post content, which is a genius addition), and the excellent customer support (Firsh is extremely generous with his time), and you've got a plugin worth every penny.