Paint an accent wall.
Color makes a big difference in your space. Just painting a wall a nice blue or green for example, can add visual interesting and promote a more thoughtful mood.
Use a wireless keyboard and mouse.
A wireless keyboard and mouse can be used by the students to control the instructor's computer to demonstrate what their group has done.
Use a wireless clicker.
Use a wireless clicker to go through a presentation while you are walking around room.
Use small whiteboards for activities.
You can have small whiteboard made at Home Depot or Lowes. They will cut them for you and it costs less than $15 a board (at least in Arizona). These are useful for students to work together on at their tables and then to present to the class with.
Rearrange your furniture.
Simply rearranging your furniture in a more collaborative manner can promote group work and conversation. For example, create circles or groups instead of rows.
See if there is furniture in surplus you can use.
If your furniture just isn't working, see if surplus at your school has some furniture you can use.
Install Apple TV.
If you have a compatible projecter, consider installing Apple TV for $99.