I tried lots of plugins for simple popups on my site to appear over text. Many of the other plugins out there were really for advertising and not for informational popups.
This did exactly what I wanted. Easy to costumise, doesn't take over the screen or cause nuicance for users of the website.
You can see it in action here: http://kimmagedsc.ie/resources/research-into-practice/ (click on the word 'Abstract'