WP Lightbox 2 is awesome tool for adding responsive lightbox effect for images and also create lightbox for photo album/gallery on your WordPress blog
Lightbox is the perfect tool for viewing photos.
Uji Popup - Create your custom popup.
Easily turn users into cash using Popup Maker - the most versatile & expansive popup plugin for WordPress!
PopupAlly allows you to create advanced popup signup forms in under 5 minutes without the need to deal with messy code.
Easily create a popup for your WordPress site.
Plugmatter Optin Feature Box is the Only List Building Plugin that Allows You to Create High Converting Optin Feature Boxes for Your WordPress Site.
Supercharged WordPress Popup Plugin. Best way in the world for you to create unique unblockable WordPress popups to grow your list of subscribers!
Email opt-in widget that gathers visitors’ emails while they surf your site. Creates email collection popup in bottom right or middle of screen.