Christmas Crafting in no time by Clare Youngs has some brilliant relatively simple ideas. I've made twig reindeers (bits of twig stuck together with superglue with a little ribbon tied round its neck.
Gift-wrapped soap. Buy a multipack of soap, wrap in plain paper (brown, white, red whatever) and then cut out an inch small strip of some fancy paper and wrap that round, tie with silver string with a little sprig of something (pine needles?) or small beads.
Kirstie Allsopp's thing she did with the modelling clay? White modelling clay (she used diferent colours, but more pricey) roll out, cut out hearts, stars, etc using cookie cutters and stamp 'JOY' or 'NOEL' or whatever into the clay using metal letter stampers (can get them on ebay or hobbycraft). Put a hole in the top and when dry thread some festive ribbon through.
Something I've done was get some beads and some thin wire and make round shapes or hearts, and use those as tree decs. Or even buy some feathers or whatever. I love felt decs though too. The Clare Young book has some lovely ideas for felt decs.
Christmas cards in a pack and matching gift cards. Even wrapping paper. (plain paper, make a festive stamp and stamp the paper). Simple card designs, like a glitter tree - just use a pritt stick to zig zag a shape of a tree/triangle and then sprinkle over some glitter. Get stamp for inner saying Happy Christmas for inside.