Most vacuum cleaners come with attachments, but these are often too large to clean your keyboard or parts of your computer. You may be able to solve that problem with the nozzle from a sauce bottle.
Tumblr user mintfish points to this clever solution. Not every sauce bottle will suit (see the picture for a suitable example), and you'll potentially need to use tape to attach it, but with the right set-up you can use it to vacuum small areas such as the spaces between your keys. Of course, there are plenty of other options for keybord cleaning, too.