The new 2300AD from Mongoose is out:

Download the PDF from here: http://rpg.drivethrustuff.com/product/100670/2300ad

More Mongoose 2300AD stuff on the way: http://www.mongoosepublishing.com/rpgs/traveller/2300ad.html

I'll also reccomend the DVD with the old 2300AD material from farfuture.net: http://www.farfuture.net/Contents%20CDROM%202300AD.pdf

You get all the books AND the relevant Challenge Magazine articles. Great value.

Finally there is the 2320AD PDF: http://www.travellerrpg.com/2320/

You can't actually buy the PDF anymore, but you can find if floating around for free if you take a look. Was never printed. Only PDF.