David Cameron has said the coalition will use some of the spending cut ideas suggested by members of the public and those working in the public sector.
Downing Street says about 100,000 ideas have been submitted to the Spending Challenge website.
Ideas include encouraging volunteers to form teams of "civic gardeners" and reduce the demand for council staff.
Ministers are considering the ideas, which could be included in the coalition's Spending Review in October.
Around two thirds of the ideas submitted to the Spending Challenge website come from public sector workers.
Suggestions include getting cheaper mobile phone contracts across government, and switching government and public service computers to run on free Linux and open source software.
Rate the ideas
A junior doctor has suggested making criminal record checks portable so NHS staff do not have to reapply each time they move to a different trust.
Mr Cameron, who faced a protest from around 100 public sector workers as he sought to expand on the ideas at a "PM Direct" meeting in the Brighton, is said to favour ideas matching his Big Society ethos, such as the gardeners one.
He told the meeting: "I want to make sure we take as many people in our country with us as we do that.
"That's why we issued this Spending Challenge. We have had 67,000 e-mails with ideas and letters from people within the public sector coming up with some great ideas. Some big ideas, sometimes quite small ideas, but great ideas for how we save money."
Mr Cameron added: "Someone else working in the immigration system said it is mad that when people appeal against a visa decision, even though that appeal may cost £10,000, that appeal is entirely free. Something else we can change."
The Spending Challenge website will stop accepting new ideas next week, and will instead allow the public to rate some of the ideas submitted.
Public sector unions have already described the exercise an "outrage" claiming that workers are being asked to contribute to their own sacking.