For people who may have some gross motor movement (say enough to hit a switch with a hand, arm, elbow, foot etc but not to 'steer' a joystick or trackball), who still want to try and use them as much as possible a multiple switch box maybe a solution to controlling your on-screen cursor.

First you will need a switch box to connect switches to. The switch box has a USB end usually which connects to your PC.

Here are a few examples:

Joybox - connect up to switch function switches (drag lock, right click etc) PLUS 4 directional switches.
http://www.smartboxat.com/joybox.html

Inclusive Multiswitch - up to 6 switches
http://www.inclusive.co.uk/catalogue/acatalog/inclusive_multiswitch.html

If you need more switches but dont want loads of wires everywhere you can purchase something like starswitch:

http://www.qedonline.co.uk/catalog/product_info.php?cPath=83&products_id=260

or RJ Cooper has a big button box containing directional control and one or two switches, you can choose to have them mounted to left or right.
http://rjcooper.com/mouse-button-box/

For those who would like a bit more directional control but struggle with standard joystick/trackball the 'MOOZI' maybe the solution for you.
http://www.qedonline.co.uk/catalog/product_info.php?cPath=83&products_id=542
(can also be used to steer an electric wheelchair)

You could have this plugged into one switch box and a single switch for something like drag lock or one multiple input switch (eg star switch) for programming extra functions... copy, paste, bookmark etc