jaz0nj4ckal. Welcome to Traveller!
I started playing Traveller in 1982 and my friend who introduced me to the game had the big fold-out map of the Spinward Marches. So it has always been my favorite area of known space. As others have said before, the SM's sector is kind-of like the "Wild west" of the Imperium. It's a nice mix of civilization, danger, back water worlds, lost alien technologies, pirates, smugglers, honest and dishonest merchants.
It is not absolutely necessary, but if I were you, I would get the Spinward Marches supplement along with the fold out map - large map is sold separately unfortunately

The websites already mentioned are great, but to me it's so much better to have a map folded out on a table in front of all your friends with them searching worlds and plotting their next move. I'm not sure if you can print directly from Travellermap.com.... Anyone know if you can print from that site???
I have also purchased the Alien supplement "Alsan" along with the large fold out map. This part of known space is called the Trojan Reach sector, just Rimward "south" of the Spinward Marches. My players started adventuring in the Spinward Marches but are now heading deep into the Trojan Reach.
I will also point out that T20 released a large pdf version of the Gateway Sector (on the other side of the Imperium) You can still use the Mongoose rules but use any previous released settings. The Traveller Universe is huge, so have fun!