The charity hit the headlines after its protesters affixed solar panels to the roof of Deputy Prime Minister John Prescott's house.
The protest was used to draw attention to the emission of greenhouse gases by British homes in the run-up to the general election.
Human rights charities, meanwhile, struggled to gain coverage of their work for tsunami relief for the first time since the disaster.
Both the Red Cross and Amnesty International saw their number of mentions drop, although the overall reduction in coverage given to NGOs meant each jumped up a place in the table.
'The impact of the tsunami on media coverage of NGOs has significantly decreased,' said Toby Lincoln, researcher at table compiler Infonic.
'Along with the media focus on the election, this means there was less attention in the media on NGOs than in previous months,' he added.
The RSPCA was this month's biggest riser, jumping back into the top ten for the first time in two months.
The charity highlighted the £35,000 cost of keeping dogs that had been locked up in a van in Manchester, while the owners' appeals against a conviction for cruelty were being heard.
Unicef also crept into the top ten for the first time since February for its attempts to stop the spread of the Marburg virus in Angola.
REPUTATION MONITOR - 21-27 September 2004
Ranking NGO No of mentions
1 Greenpeace 87
2 Red Cross 73
3 Amnesty International 66
4 Friends of the Earth 64
5 Cancer Research UK 59
6 RSPCA 50
7 Human Rights Watch 47
8 RSPB 45
9 UNICEF 43
10 Oxfam 43