All these WordPress themes are free and use post thumbnails so little if any tweaking is needed.
Gridster Lite
Gridster is a neat and tidy grid-based portfolio theme for photographers, artists and designers to show off their work.
Hueman
A fully featured, responsive high resolution magazine & blog theme without compromise. Hueman presents what you love to write about in a visual & user-friendly way on all devices.
Fancier
Fancier is a dark, responsive theme with 4 columns. Needs some tweaks but looks promising.
Mh Magazine Lite
This is the free version of MH Magazine WordPress Theme, ideal to create amazing online magazines within a few minutes! Upgrade and support available.