Yea .. two different monitors. Mine is an older 20" computer monitor for the singer and 32" for the audience (if the gig warranted it). I have used an iPad at times, since the singer's monitor is only a foot or 2 away.
I currently use a 20 inch monitor. Back before flat screens I used a 13 Inch as a monitor & a second 13 inch for the audience for the value packages. With the larger monitor you end up putting them further away from the singers. Nobody is going to want a huge monitor right in their face. One thing I noticed is that with large screens to the audience it gets them more involved singing with those on stage. It is such a huge difference I will always use at least a 32 inch pointed at the audience.