As more and more suggestions come up, here's a little readme on what to do:
1) Check the list of wanted contribution: http://wiki.openttd.org/Todo_list
2) Check the list of commonly requested suggestions on http://wiki.openttd.org/Requested_features
2) Check the commonly requested suggestions on viewtopic.php?f=32&t=22278
3) Do a search on the forums
If you find anything similar to your suggestion there, DON'T POST. It doesn't get implemented any faster just because people are posting the same things over and over.
After that, ask yourself a couple of questions:
1) Is it just a funny idea I had, or would in improve gameplay?
2) Is it in anyway related to reality
3) Is the average user able to understand/use it.
4) If you have any experience in programming, try thinking a second how you would implement it and post these thoughts as well. One line of code often says more than 1000 words anyway.
5) Be clear and specific.