Red rubber bracelets usually are for HIV AIDS awareness and heart disease prevention. They have a variety of different messages stamped on them depending on the specific cause. They were also used for pro-Bush sentiments before the 2004 election and have been associated with anti-tobacco and smoking campaigns. In addition, after the Red Sox had their World Series victory, Red Sox red rubber wristbands that say "Red Sox Nation" became super popular.
Orange Rubber Bracelets
The orange rubber bracelets usually signify support for Multiple Sclerosis and say "I Will". There are also orange rubber bracelets that represent Tennessee UT basketball team, and other sports teams. Tennessee is notable because their orange rubber bracelets were one of the first take-offs after the Livestrong bracelet got really popular. In addition, The American Cancer Society has release orange rubber bracelets that say, "LiveFree. SmokeFree." in an effort to promote a smoking free lifestyle. Orange wristbands are also used for support of Asperger's syndrome (a syndrome that is kind of like autism), lupus, and self harm (I think this is people who cut themselves).
Yellow Rubber Bracelets
The yellow bracelets support general cancer research. Lance Armstrong originated the trend of rubber support bracelets with his "LIVESTRONG" bracelet and over 28 million have been sold. More info on the LiveStrong bracelets is here.