I like Traveller, and have played it since the mid-80s. Basically, there are two current versions of it getting support with new material -- GURPS and T20.
If your group is familiar with 3E D&D or any other d20 game, T20 might be what you're looking for. It uses d20 system, so most of the rules will be familiar. So far there is only the main handbook plus some free downloads and inexpensive pdfs on the main website, here:
Traveller RPG But the company has several setting supplements in the works (I know because I've freelanced for them), and some of the pdfs are going to be released in print versions.
GURPS is its own system, but does provide a lot of variety. You can find GURPS supplements for just about any type of modern and/or futuristic game you want to play. It's all interchangeable and compatible. I use a lot of the GURPS Traveller material as background and supplemental material for my T20 campaign.
Classic Traveller, the original version of the game, is available as a reprint from Far Future. It would mean learning a new system, but it is a very easy game mechanic. Also, most if not all of the background and setting material for Classic Traveller is usable with GURPS and T20 -- I use it all the time. In fact, some of the GURPS material is the same as the Classic Traveller material, just rewritten and (in some cases) expanded. Many of the people who wrote the Classic Traveller stuff later wrote the GURPS stuff.
I like Traveller because it is a very flexible, very adaptable game. You can create just about any type of modern or future campaign you want. You can do military-based, high combat campaigns; you can do exploration campaigns; you can do economics-based campaigns, buying and selling cargoes on various worlds and transporting it by space ship; you can do espionage and intrigue campaigns; the possibilities are endless. Just as an example, I once created a campaign based on the movie "Aliens" in which the players were Marines hunting Alien creatures. I'm currently running a campaign in which the PCs are government secret agents involved in cold war intrigue with a neighborhing empire.
One thing I've found out about Traveller is that is a very fan-driven system. There is lots of material out there on the Internet created by long-time fans and players of the game. Much of the T20 support material has been, or is being done, by fans and players of the game. It is a game that has earned a lot of passionate support from its players, who have helped keep it alive through several incarnations.