I weed the letters out based on what the cause is, what my mood is, and how recently they asked for money.
I also try to give money to organizations that my family members who died gave to (my great aunt was very involved in Shaare Tzedek in Israel, so I donate in her memory when I can).
I also try to give organizations for food. Thats the most important to me. For Rosh Hashanah, I donated groceries and meat in Israel (I think the organization is called Mesamchei Lev).
When my son was born, I donated a year worth (money wise) of formula/baby stuff to thank Hashem for the healthy baby I have. I also recently gave to a tzedaka that helps couples with fertility treatments because I had an easy time getting pregnant.
I dont give to Kollels. There are too many important places out there that need my support, and a guy learning in Kollel can go out and get a job. He is much lower on my list.