Brian fired me a link today for 30 essential programs - free or open source. 

It's a nice list.  I use a lot of them myself to various good effect.  Some I use daily, others - well, I've never been involved with filesharing, so those are simply not relevant to me. 

My list is a lot shorter than 30.  My list of programs that everyone should have. 

1.  Firefox.  It's a better browser.  It's not perfect.  If you prefer Opera, that's wonderful.  Use Opera to your heart's content, I like it too.
2.  Thunderbird.  Companion to Firefox, everyone should dump Outlook immediately.  I rarely get to make this recommendation.  If you CAN make the jump, I recommend it.  (The reason I mostly don't - I don't feel Sunbird is up to the job for integrating calendars as Outlook has.  Sunbird is MY choice for calendaring, but it shouldn't be everyone's yet.  Thunderbird is superior for just reading email.)
3.  An anti-virus program.  I'll make two recommendations here:
     AVG - Free, stupidly easy to use, it's the first choice I recommend to clients.
     AntiVir - This is a free one that's really nice too.  I'm less familiar with it, but when I've used it, it's held up very well.
     Clamwin - The AV I use.  Good for me, not for everyone.  Seems a little slow on my laptop.
4.  A software firewall.  Here, I only recommend Zone Alarm.  This one is better than any other software firewall I've used - and VASTLY superior than many I've seen paid for (Symantec, I'm looking at YOU!)
5.  Anti-spyware.  There's a big problem in the "Spyware"-fighting business.  Mostly - you don't know who you can entirely trust, and partially because anti-spyware companies are fighting amongst themselves.  (Symantec, I'm looking at YOU!)
    I strongly recommend Spybot Search & Destroy as everyone's option #1.
    I also use Ad-Aware SE.
 The reason I pick Spybot S&D first is the licence.  Ever read through dozens of pages of gobbly-gook when you install a program?  I have to.  I like Spybot's terms.  (Slight editing here)

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"Dedication Public License (DPL)
By downloading the archive, you confirm your agreement in this license.

I. Freeware
First of all, the reasons why Spybot-S&D is free:

I.a. Dedication
Spybot-S&D is dedicated to the most wonderful girl on earth :)

I.b. Binary
What do you get if you buy software? Lots of ones and zeros, nothing more. If they were distributed as art, I could understand paying it. But if the main goal of their order is to earn money - by fees or ads - I don't like it!

I.c. Conclusion
This means that I grant you the license to use Spybot-S&D as much as you like. But if you like it, I ask two things of you: say a prayer for me (and the most wonderful girl while you're at it ;) ) to your god - or whatever you believe - and wish us some luck."

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It goes on from there, but that first part is as clear cut as you can get.  I like people who write licences like that - I trust them.  And I need to trust people who are taking malware from other people's computers.

There.  That was easy.

Safe computing, everyone.