So much depends on what you're trying to do, the quality if pics you want, and if you want to run multiple cameras over an area and not just one. If you need multiple, a system that works together that will allow a single unit to handle the transmitting back to your phone will be highly cost-effective since you'll only need one cell service account.
You can buy some really base models with modest photo capabilities or you can get others that take really nice stuff. Sort of depends on if you're approaching all this with any sort of budget limitations. If you're only looking for the best stuff, there are suggestions; if you're looking for bargain basement, there are others.
There's a Cuddeback that will let you set up as many as 24 different cameras on a network. Reconyx has long been one of the superior makers and allows you to get some video as as well as photos. Spypoint is a low-priced option that works for a lot of people that don't want to tie up much money in the effort.
