jEdit
The world's most powerful editor and a pretty good IDE for too many languages to mention. Once you try the regular expression hypersearch function you won't ever look back.
Notepad2
For a super-lightweight, blindingly quick and simple replacement for Window's default editor, you can't go wrong with this baby. It's a genuine, simple replacement for notepad, unlike Notepad++, which (IMO) does too much to be really quick and simple, and too little to compete with jEdit or UltraEdit32.
Beyond Compare
While jEdit has a comparison plugin - jDiff, it doesn't begin to
compare (sorry) with Scootersoftware's minor masterpiece. This will compare directories, files of all types and all kinds of archives (even war, bin, cat and jar files, to name but a few). Old versions are available for free.
Fiddler2
While some might argue this isn't really in the domain of a typical sysadmin, I think understanding exactly why a page is throwing an HTTP error 500 code, or why a certain component renders slowly or never loads at all is pretty useful, especially since the post-financial crisis sysadmin typically has to take on many jobs that would normally fall to developers, webmasters and software engineers.
Radmin
While there's are a lot of remote control software out there, I've never tried one that is quite as good for remote administration of multiple Windows clients. Free is great, but sometimes, you only get what you pay for.
ZipGenius
While the version for 64-bit Windows 7 leaves a lot to be desired (they are still working on shell integration), ZipGenius rules on 32-bit Windows systems. Incorporating 7-zip binaries, as well as many others, such as C.A.K.E, UnRar and UnAce,there is little or nothing that ZipGenius can't open. It's missing the ability to simply GZIP files (it TARs and GZIPs them instead).
PuTTY
A free Telnet and SSH client that still can't be beat for its simplicity and power. Put it on a stick and shake it at every problem you've got.
Filezilla
The ubiquitous FTP client that's so obvious that we forget it's even there. There's a lot of competition in this area, but its still a winner for me. It's my
FTP server of choice too.
phpMyAdmin
OK, so not all sysadmins use
MySQL - but they should. There's every reason to have at least one instance of MySQL running, most sysadmins these days are at least part time solution developers. If there's a reason to have MySQL, there's a reason to have phpMyAdmin.
SQuirrel SQL Client
For every other DB, there's SQuirrel SQL. Oracle, DB2, SQL Server, MySQL, Derby, posegreSQL - you name it, they have a driver for it.
Eclipse
There are so many plugins for Eclipse, and so many tools that can run on its framework, that there is no way a serious sysadmin should be without this. Want to put together a website with some
PHP? Try the PHP perspective. Need to glue some disparate applications together, use the perl perspective. Got JVMs heapdumping? Use the memory profiler, load up some verbose gc logs and away you go. I could go on, but you probably get the picture. You can say it does a bit of everything, and none of it very well. But it is flexible, and its free.
Clonezilla
Backup and clone a system to many computers thanks to Clonezilla's use of multicasting. No need for the slavish one-at-a-time approach that can make a sysadmin suicidal, and that can only be a good thing.
LogMeIn
This has to be the biggy. You're offsite. You're online. You need to assist your client right now. They could be 40km away, or they could be 4,000km away. This one is priceless. Maybe you have to get to your work desktop while working from home without access to a VPN. If you're company allows it, use it. If it doesn't, invest in one of the many expensive alternatives - WebEx, Sametime Unyte, AOS.
Yes, I know, I'm missing something. Please tell me what it is and where to get it.