I also recommend Starships Unlimited:
http://www.apezone.com/
Unfortunately I find the latest version less fun than the original (which is reviewed here:
http://www.the-underdogs.org/game.php?id=2370 ). The graphics are nicer but you no longer find interesting stuff on every planet. This was probably done to reduce randomness and make the game last longer, so if you agree with those goals you might like it anyway. I personally still play the old game because it's different each time you play and you can finish a game in one sitting.