Props are great to liven up a presentation and make things more tangible for your audience; even if they can't actually touch the props you bring. If you are doing a product introduction or demo of sorts, I strongly recommend to bring your product with you, if it fits on the stage somehow. Seeing a real person interacting with it, holding it, or simply standing next to it (if it's really big) will give your audience a much better idea of the size and use than any product photo on a slide could do. So if the goal of your presentation is to introduce and eventually sell a product, this should be a no-brainer.
If you still need convincing, watch Steve Jobs introduce the MacBook Air (remember the manila envelope?) or, a personal favourite of mine, the iPod nano:
Ever wondered what this pocket is for?
Props Should Be Relevant to Your Talk
What about other props? As a - rather obvious - rule of thumb, everything you bring on stage should have a purpose. Don't bring things for decoration (leave that to the stage designers) or just to make your company or product name more prominent (such as banners). Those would only distract from your actual presentation - or simply be ignored, in which case it was a waste of time and effort to bring them.