On behalf of the OpenTTD team I am proud to present you OpenTTD 0.5.0 (the final version this time). Those who have been us since the release candidates, we thank you for your diligent testing and bugreporting. For the users who are only now venturing to upgrade from 0.4.8, you will see a *LOT* of changes, all for the better. The various RC's have already talked about this, but let me restate the biggest changes since 0.4.8:

We have a new fast, robust and flexible pathfinder, electrified rails support, a brand new terrain generator, full UNICODE support and better multiplayer. NewGRF compatbility (modding) has been greatly enhanced with support for changing stations, adding sounds, more vehicle sets, etc.
The smaller feature- and buglist goes on and on, but we'll let the user explore this. All users of 0.4.8 are encouraged to update to this new release.

Please read the full announcement at the forums as it contains important information for Win9x/WinME and international users.