For years surplus guns have been a great way to get into the gun hobby for cheap. This started with the release of the WWI & WWII weapons in the 1950's & 60's. At one time you could order a surplus M1911 from the CMP for $15 and have it delivered to your door (sans dealer paperwork). The surplus 1911s are gone, as are the 1903 Springfields, but thanks to the Lend-Lease program many M-1 Rifles and Carbines are available.
Most of the M-1 Garands will be of Springfield manufacture, but you may get lucky with a Winchester, of course WWII vintage Garands are the most sought after
When it comes to the M-1 Carbine, there were many more manufacturers, ten war time producers with Rock-Ola Juke box company versions being the rarest, there were also paratrooper models with folding stocks (designed to fit in a thigh mounted holster)
There are other WWII vintage guns available, you can easily find the Soviet Rifle known as the 91/30 Mosin-Nagant. These are available in arsenal refinished condition and are great shooters. The best part is you can find them for $100-$150. Again War time built guns are more desirable as are the older hex receiver guns
Another war time rifle that is still plentiful is the Japanese Arisaka rifle. Several variations exist and some collectors search for models known as "last ditch" guns, these were hastily built guns during the final days of the war when parts to complete the guns were scarce, so some "improvising" had to be done. Again war time dates are better as are finding one with the "mum" still in place. The Japanese Government put out an edict that all surrendered guns must have the chrysanthemum flower ground off. The chrysanthemum was the symbol of the Japanese empire and they thought it would be sacralidge to surrender a gun with the mum on it. The ones with the mum intact either slipped through the cracks or were taken from dead Japanese soldiers and brought home by the US GIs.
Mauser K-98s are still available as are the many variants from Argentina, Turkey, Spain, Siam just to name a few. Mitchell's Mausers has restored WWII vintage guns for a very reasonable price (http://www.mauser.org/). They also stock Lugers and Walther pistols.
It is getting difficult to find an original, unmolested one as many were sporterized during the 50's & 60's.
Speaking of Walther pistols, these are also in plentiful supply, good luck in finding a WWII vintage with the Nazi proofmarks, but they are out there. Most of the P-38 and P-1 pistols available are post war versions with aluminum frames, which spent time as police duty weapons in Europe.
If you have your heart set on a WWII vintage handgun, you may be able to get a Tokarev pistol to suit your desire. They were made by the Soviet Union during WWII and many (if not all) of their Eastern Block states. The most common are the Romanian and Yugoslavian. Import rules now require a safety be installed, so if you find one without the safety, it is a good score.
China also makes them (in 9mm as well as the 7.62 x 25mm) Ammo was once plentiful, but has since dried up somewhat. There are some commercial rounds available, but the price is a little on the steep side.
The Russian 1895 Nagant pistol is also easy to come by, not all that much fun to shoot, but they are cheap and very unique.
More guns from Eastern Europe include the CZ guns, both the CZ 50 & CZ 52 can be found from importers for reasonable prices
You can also score a surplus 9mm Makarov pistol from the former Soviet Union. They are also available new.
Be careful what ammo you use as these do not shoot the standard 9mm luger round, they use the Russian 9 x 18mm, some of the new ones can be had in .380 as well (9mm x 17mm).
Another surplus gun that you can get from the "Mother land" is the Simonov Karbine, also known as the SKS. The Russian, North Korean and North Vietnamese ones are the most desirable, but the Yugoslavian and Albanian are also very popular with collectors. Starting in the 1990's the U.S market was flooded with Chinese made SKSs, some of which were built on Soviet tooling and were of really good quality.
An agreement made during the 1990's allowed for the importation of fully automatic AK-47s, although the guns had to be "de-milled" and the full auto parts removed, they were sold as "kits". A cottage industry sprang up to supply parts to rebuild these rifles into working semi-auto, legal versions. The kits came from Bulgaria, Romania, Albania, Hungary and even Russia.
Under the same concept you can score an FN FAL kit
When discussing surplus guns we cannot forget the domestic market of used Police guns. Most of the revolvers are all gone (although J&G had some S&W model 64s a few months back), most of what is out there are surplus semi-auto pistols. Sometimes a deal can be had, especially if buying in bulk.
Used Glock 17s and Beretta 92s are out there, many times the guns were carried a lot, but shot very little.
There are many others out there, the PPS, & PPSH, Suomis, FEGs, etc.. If you are interested in getting a surplus gun, pick up a copy of the Shotgun news sometime.