Idea #1 Replace a nightstand with a desk with a lamp on it. Your guest can still put their purse or cell phone on the desk, using it as a nightstand, while the other 28 days of the month you can use it as a designated place to sit down and go on the internet. (For even more space, replace both nightstands with dressers.)
Clean Eclectic Family House Tour on Apartment Therapy
Elle Decor via Amber Interior Design
Idea #2 Turn the closet into an office.
Apartment Therapy via graceandivy.wordpress.com
Idea #3 Get a storage bed.
This West Elm "Pivot" storage bed lifts up easily for extra storage
The Pottery Barn "Cynthia" storage bed comes in white as well, and features drawer storage
Idea #4 Frame the bed (even if there is a window behind it) with two tall and narrow shelving units or built-ins.
Schibstedforlag.com via decorpad
Massuco Warner Miller design
Idea #5 Go up. Whether you have a desk in the room or not, using shelves to put things on, hanging paintings or photographs, or hanging up a corkboard utilizes more space in the room.
Chris's Childhood Bedroom via Apartment Therapy
Idea #6 Turn a whole wall into storage.
Casa Del Mar via Cococozy