I don't always call the roll at the start of the lesson for some of my classes, as by mid-way through the lesson I usually know who is there and who isn't. We complete our rolls electronically and so when there's an opportunity during a lesson, I complete it then - either on the school laptop or on my iPod Touch as I wander around. However, I do call out the roll for my new Year 7 classes at the start of the lesson as I don't yet know them so well.
Over the past couple of weeks we have been learning numbers and so rather than have the students call out 'Hai Sensei' (as in "Yes Teacher"), I had them call out their favourite number in Japanese. This has worked really well and so from next week I plan to do this for Year 8, who have been learning the subjects in French. They will be asked to call out their favourite subject in French.
So next time you are calling the roll in your language class, pick a topic for the week and have them call out a word from their vocab list in the 'Target Language'. You could do it sequentially for something like numbers or you could place limits on the number of times a particular word is called out. Please share your ideas in the comments.