I've played 2300 using 2300AD, but most of the time I used the Traveller New Era set, and borrowed liberally from Twilight Sourcebooks. Twilight Nightmares was an especially good source of stuff. Dark Conspiracy was another games that I cribbed from, mostly for new and gruesome Pantapod artifacts. Not too long ago I ran a game that used Traveller starships, 2300 setting, and Cyberpunk 2020 rules.
Of course, my most recent games have been D20...
Colin
2320AD writer