which countries produce the most amount of space junk?

USA...

And the order is:

USA

Russia

European (Here includes all countries who have membership in ESA).

China

India

Japan

There are 35,000 objects a half inch or larger. I don't think there is a way to quantify which junk is from which country since that 35,000 includes pieces of pieces of components (rocket boosters, etc) that are in orbit. Obviously most of it has to come from either the US or Russia/USSR. It's become a real concern since even a tiny object hitting a space station or shuttle can cause damage or worse, kill an astronaut out on a space walk.

One of the most famous pieces of space junk is a glove that floated out of the capsule during Ed White's space walk in 1965. You can see the glove floating out and away in the film of the walk.

EDIT - I'm not sure why people are saying China when the US has been leaving junk in space for over 50 years. So have the Russians. Even if the Chinese are "sloppier" when it comes to their launches, it is nowhere near as active as the US program in the 60's and a lot of that crap is still floating around, including a Vanguard booster from 1958.

Which countries have (or had) the biggest, most developed Space Programs?

United States and Russia. China and the European Union are starting to catch up. Japan is still in the rear.

Most other countries do not have space programs, and could not have put any "junk" into space.

China currently - they have, other than NASA or the Russian federal space agency, not yet adopted a space debris mitigation strategy. Also, China lately produce a large amount of space debris by destroying a Chinese satellite in sun synchronous orbit with an anti-satellite missile. (Before you complain, the USA did that already twice, but had been smart enough to do that with low flying satellites. This ensured that the debris was captured by Earths atmosphere quickly, while the Chinese debris will disturb operations for thousands of years)

The other big spaceflight agencies have all rules about how to prevent debris, which are pretty similar, but have small differences in details. If you ever design a satellite or a launch vehicle, you will have to follow such rules and especially if your satellite is planned to be able to be launched by launch vehicles from different countries, you need to make sure your satellites follows all rules.

It is not like you will get fined for littering if you don't follow such rules, but if your debris damages another satellites, your country will have to pay the damage. And be sure, the "tax payer" will make sure that he does not have to pay for you breaking debris rules - you will get the bill eventually.

One way to prevent a large amount of debris is preventing rocket stages from exploding. After launching a satellite, these stages are also in Orbit and have still a large amount of fuel inside them. If you let such stages become space debris (=not reacting to ground commands anymore and thus not able to make controlled maneuvers), you have a high chance that after some months or years in space, the stage explodes (the engineering term is fragmentation) for example because of gases expanding inside the tanks while getting slowly warmed, or other space debris hitting the stage. Even the batteries inside a satellite/rocket stage can explode, if you don't control the temperatures inside the vehicle.

Such fragmentation events are the biggest source of space debris, and had shown their danger already. a large fragment of a chinese rocket stage, that had exploded ten years earlier, destroyed a French military satellite. I have seen a synthetic aperture radar image of the satellite after the impact, the damage was easily visible.

For preventing such events, the big commercial launch providers make sure today, that the rocket stages are completely drained of fuel after the launch, if possible by using the rocket engines again to bring the orbit of the stage closer to Earth. Also, batteries are also opened to space, which means the rocket stage will quickly run out of electrical power and become space debris itself, but it is easier to follow a single large rocket stage with ground radar, than thousands of small and large fragments.

Russia is also responsible for some large amounts of space debris, especially their nuclear powered ocean monitoring satellites produced large amounts of small metal salt balls, ironically when they ejected their nuclear reactor cores into a grave yard orbit for preventing the reactor cores from becoming a uncontrolled hazard. The NaK salt was used as powerful reactor coolant and today forms hundred thousands small spheres in space, up to 5 cm large. At a typical collision speed of 14 km per second, it does not matter if the NaK is liquid or solid, it would cause serious damage on a satellite.

The USA had also not been lazy in space, but had initial debris mitigation strategies already in the 1970s after a US scientist showed how too much space debris can result in a runaway chain reaction of collisions, which will make it impossible to do spaceflight from Earth.

The top three "countries" by mass in order are:

The United States

Russia

China

USA produce the most amount of junk - full stop. And they seem to be somewhat proud of themselves.

china

USA