Qustion answers

Que. 1)  Which countries are trying to explore the space right now?

Ans= India, China, Japan, and the European space agency
as well as Russia and the US.

Que. 2)  How much money is spent on space exploration?

Ans. =  You can see the NASA budget over the last 40 or so years here. In 2005 NASA had a budget of $16.2 billion, this includes not only the human spaceflight division, but also other engineering projects, and science funded by NASA. The total federal spending budget in 2005 was on the order of $2 trillion ($2000 billion), making the NASA share 0.8% of the budget. By comparison roughly 19% of the budget was spent on the Military, 21% on Social Security and 8% went to paying interest on the national debt.

more info on this Que.

The ESA budget for 2005 was 2.98 billion euros (about 3.5 billion dollars), but many European countries also have their own space agencies which are independently funded, so it's not strictly a fair comparison.
ESA and NASA are by far the highest funded agencies. The Russian space agency has an annual budget of $800-900 million dollars (and it's about the same for India), Japan ~1.8 billion, China ~1.2 billion.
To be fair though, we need to compare these numbers to something which tells you about the wealth of the nation - for example the Gross Domestic Product. The CIA world factbook is a great resource for information like that.

	GDP in 2004	Percent spent on space
USA	11.8 trillion	0.14%
Europe	11.7 trillion	0.03% (not inc. individual agencies)
Japan	3.7 trillion	0.05%
China	7.3 trillion	0.02%
Russia	1.4 trillion	0.06%
India	3.3 trillion	0.03%

It's also interesting to work out how much is spent per person:

	Popn	Space spending per person in 2005
USA	0.3 billion	$54
Europe	0.6 billion	$5.80 (not inc. indiv agencies)
Japan	0.1 billion	$18
China	1.3 billion	92c
Russia	0.1 billion	$9
India	1.1 billion	82c

Considering the total budget for the world for space (~25 billion dollars), the total amount spent per person is $3.90 (working on 6.4 billion people), and the pecentage of the GDP of the world which is spent on space is roughly 0.05%.

Que. 3)  Why hasn't NASA gone back to the moon?
 
Ans. = The main reason is funding - going to the moon is very expensive. NASA gets its money from the United States Congress, and in order to go to the moon again they would need to make a compelling case to Congress as to why the program should be funded. This is not something that would have been easy to do in the 80's and 90's, or today, for that matter.