I have a small monthly DD to Cancer Research. I do sometimes have my doubts about its worth as they often keep writing to me either thanking me for my continued support or asking if I can up my DD. All this costs them money. I just feel that they should take my cash, use it for research and get on worth it, I don't need feedback every 2 months on cancer rates etc.
Macmillan Cancer Support - They do an amazing job, not just for the sick, but the families too.
The chances are, a lot of us will be using them sometime in our lives. That reason alone is worth a small donation I reckon!
I personally don't have an issue with heads of big charities being paid large salaries as long as it's comparable with similar positions in other sectors . You cannot IMHO expect a talented individual to head up a large global charity for free or minimum wage or whatever. And it may well be the case they bring more value to the charity than their salary.
I give to Chesnut Tree House each month, the club regularly support it too - based in Sussex, helped out a relative too.
http://www.chestnut-tree-house.org.uk/