a. mailwasher. this is free if you have just one email account to check. It learns over time and remembers your friends, blacklists and lets you clean inbox before downloading anything. I use this to assist in the fight. 
b. Spamfighter, POPfile, and Spampal. These are all free and work in similar fashion. They each take some effort to educate them, but they work. It's worth investigating each for features. 
c. Thunderbird has a good junk tool, but needs your participation to identify both good and junk mail. AND, if you're using spamassassin, POPfile or Spampal (and a couple of others), you can tell TB that in the Junk Settings section and it will honor what those products identify as spam. 

No easy answer here; it's a forever battle. Some possibilities: 1. does your email provider provide any spam tools? For example, some provide spamassassin tool. It doesn't hurt to ask. 2. There are several free (and fee) tools. I'll just speak to a few free ones. a. mailwasher. this is free if you have just one email account to check. It learns over time and remembers your friends, blacklists and lets you clean inbox before downloading anything. I use this to assist in the fight. b. Spamfighter, POPfile, and Spampal. These are all free and work in similar fashion. They each take some effort to educate them, but they work. It's worth investigating each for features. c. Thunderbird has a good junk tool, but needs your participation to identify both good and junk mail. AND, if you're using spamassassin, POPfile or Spampal (and a couple of others), you can tell TB that in the Junk Settings section and it will honor what those products identify as spam. Tip: Turn off the feature that allows remote content at tools>preferences>privacy&security. Then, you can add exceptions when receiving 'friendly' mail.