You did not mention what you are projecting. Video, Power Point, IMAG, Photos etc. What is the source? Projector prices are ridiculously affordable right now for smaller venue stuff. If you are a bit more specific some people on here can probably steer you in the right direction.
Along those lines, anything about the general use and conditions would help. Along with the content and source factors Ben noted may be factors such as the ambient lighting conditions, are you always able to darken the room or might you have to deal with the lights being up or even outdoors? In addition, are you thinking front or rear projection and in either case how much room from the screen to the projector is likely to be available?
On the screen or image size, the 8'x8' image you noted is not a standard video image, which might be 8'x6' or 10'-8"x8' (4:3 format) or 8'x4'-6" or 14'-3"x8' (16:9 format) or maybe a similar 16:10, 15:9 or 5:4 format.
Finally, do you already have a defined budget or are you trying to establish the budget?