Blow-Up is great for your portfolios! You can also use this theme in a website made with another theme, just to show your images fullscreen. The Blow-Up theme resizes images to fill browser while maintaining image dimension ratio. Adding images is really very very simple with the free Slider stacks or snippets. There's an example snippet with links to three tulip images in the downloadfile, so you can start immediately.
There are 6 themes in the download file with a dropdown or a side menu and both with a YouTube version and (NEW!) a Flickr version that pulls all images from Flickr: • Blow-Up with a side menu • Blow-Up with a dropdown menu • Blow-Up Flickr with a side menu • Blow-Up Flickr with a dropdown menu • Blow-Up YouTube with a side menu • Blow-Up YouTube with a dropdown menu