Habitat for Humanity is making a difference for good in the world... http://www.habitat.org/
Second Harvest is doing good work in the food bank area... http://www.secondharvest.org
Mercy Corps is doing good things... some of my friends who dislike the Red Cross and/or the Salvation Army for various reasons give to them, and after doing a bit of research, I can see why... http://www.mercycorps.org/
Doctors Without Borders does good work... http://www.doctorswithoutborders.org/
Heifer International does, too... http://www.heifer.org/ (plus it's just pretty cool to give a family a critter that allows them a better livelihood, you know? Critters are cool.)
There are a set of six websites which I try to click buttons on every day...
You can click buttons for free and goods/money/services are donated to those causes. Setting one as a default homepage in a browser reminds me to click each day... it's not just that it's a free way to help out, but it's also a conscious reminder that I'm part of the larger world and that I can make a difference in it when I sit down at the web. They also have affiliated stores... http://www.gearthatgives.com/
That reminds me... about debt stuff... do you know how much your own credit card companies donate to the Republican Party each election cycle? What about the bank where you have your checking or savings account? I did some research on that last spring, got pretty angry/depressed, and realized I needed to make a significant effort to deal with my debts and my investments to make sure that megacorps weren't using my money or debt to advance their agendas which contradict mine.
Oh, and when I remember to, I check out where I'm spending my money to see if they are green or blue rather than red (and yeesh, color-coding sucks, but, hey...) I try to buy environmentally-conscious or Democrat-donating rather than Republican-donating:
And I just spotted another interesting place... http://www.alonovo.com/about
I get action alerts by email from these:
NARAL ProChoice America http://www.naral.org/
Planned Parenthood http://www.ppfa.org/
American Civil Liberties Union http://www.aclu.org/
NRDC BioGems http://www.savebiogems.org/
The Nature Conservancy http://nature.org/
I also signed up to get news emails from my elected officials a while back... the Congressional folks all have such mailing lists, linked off their official websites. I haven't yet done the same for the state representatives or local government stuff, but I probably should.
After seeing image after image online of poor black people struggling for survival, and sometimes not making it, in New Orleans, I couldn't help thinking about the United Negro College Fund http://www.uncf.org/ and that also led me to the American Indian College Fund at http://www.collegefund.org/. I'm still looking for useful organizations for poor white folks and women to get help to pay for college.
V-Day has a press release with information about organizations assisting battered women in the Katrina disaster areas. From that page: "Following Hurricane Andrew in Miami, spousal abuse calls to the local community helpline increased by 50%. The Missouri floods of 1993 saw the average state turn-away rate at shelters rise 111% over the preceding year and an overall 400% increase in need for services." Numerous shelters in the gulf coast region need help to rebuild, and that press release has good links and info.
You can locate blood drives by US ZIP code at http://www.givelife.org/.