I have been looking for one myself and after surveying about a dozen, the one that looks the best for me is the Plugable 250X (link below). I like it because it has magnification from 0X-250x so you can get images of entire beads instead of just a small section. Of course, it all depends on what you are going to use it for. There are a lot of products out there and at quite reasonable prices. Definitely check the reviews as they are quite eye opening on some of the scopes.

https://plugable.com/products/usb2-micro-250x/