Via online galleries on my Photoshelter site. I started with Photoshelter with the lowest level that allowed eCommerce sales of prints directly from the galleries. I'm at the full Pro level now with more than 75% of 1TB of gallery images up there.
It makes it easy and fast to get images to clients, particularly clients who traveled from out of town for beach portraits or weddings. I can also give multiple distributions via email addresses or group passwords.
For one-offs, or early in establishing business, USB drives are my recommendation. But online distribution gives so many advantages that I won't do physical media again unless specifically requested by the client.
1D Mk IV, 5D Mk III, 5D Mk II, 6D, 7D, EOS 55 (film), EF 17-40L, EF 24-70L Mk I, EF 24 f/2.8, EF 35 f/1.4L, Sigma 35 f/1.4, EF 40 f/2.8, EF 50 f/1.4, EF 50 f/1.8 Mk I, EF 85 f/1.2L, EF 100 f/2.8L, EF 135 f/2.0L, EF 70-200 f/2.8L Mk II, EF 300 f/4.0L IS, EF 300 f/2.8L IS I