I mainly use an Aldi Maginon camera (£79.99). I bought mine around this time last year so they may be having them in soon. If you place your camera on a brick or something similar just above the ground you should be able to tell whether or not your visitors (of the hog variety!) are male or female.
Glad to know that someone else likes magpies and their clever antics. I know that they have a bit of a bad reputation, but they eat side by side with all the other birds in our garden with no issues. It always makes me laugh how they will check to see if anyone is in the kitchen before they come up to the dish outside the back door to steal the food.