I’ve got a monopod and at first I didn’t like it. But then I got a ball head (essential for a monopod) and read up on how to use it, and now it’s good for helping to cut down shake when using long zooms. I suppose it’d also be good for landscapes and the like, not really tried it. It’s quite a subtle tool. I’ve found I can brace it against things with my body to get pretty stable positions, and it can be much more convenient than a tripod I reckon.
Other than that, a polarising filter perhaps? Although that could be more $.
But if they are a newbie, the books will help far more than anything else!