For flash drives, click the remove hardware icon in the taskbar (bottom-right) once with your left mouse button. A little menu will appear. Click the item you want to eject. It'll tell you it's safe, and now you can pull it out.
For multi card readers, when you want to take out a card, go into My Computer, find the drive you want to take out, right-click the icon and click eject. If your card reader has a LED, it might flash a bit to show it being unmounted. Pull your card out. The reader itself should still work and be shown in My Computer.