First off, pretty much anything in the range of aeronautics and space engineering is going to kill because NASA is gonna be at the ISEF looking at projects in that category so with a good project, and a great paper your looking at a chance of a lot of prise money and possibly full ride scholarships. Unfortunately, i have nothing for you on that matter.
A pretty good plant science project(if done right) would be to set up a bunch of plants, soy beans would be your best bet, and show the effects of UV rays and the different types of UV rays (UVA, UVB, and UVC) then put red die on one set of soy beans and show how it reduces and almost eliminates the effects of UV rays (because the red cancels out so much of the UV) so you will have 3 sets. the control, with nothing but artificial light, one with the UV rays (use things like tanning lights and im pretty sure they have specific lights for this) and then another with the UV rays and red die on the plants. This demonstratives how soy beans grow with the high levels of UV rays with the depletion of the O-zone layer. Great Ag. Science project.
Oh Oh and also test each set of plants for stress. To do this, after all the testing is done on the plants take a hole puncher and take samples of the leafs and test them for nitrogen, the more nitrogen the leafs have, the more stressed they are.
If you like the idea and wanna ask questions, email me
iv been doing science fair for a long time.