Scott Hanselman has been putting together a great list for the past 2 or 3 years of some of the best tools for developers/power users in his opinion. Its a pretty comprehensive list and I suggest you take a look at it. I consider myself pretty up on the latest tools around but there were a few on his list that i didn't know about and definitely will check out.
Some of my personal favorites from the list are:
I find myself using this more and more. I used to be a TextPad man, then i switched to UltraEdit (both great products by the way). but for the price of FREE, you can't beat Notepad++. It does everything I need from a text editor.
I don't think i really need to elaborate on this one. If your not using it, you sure as hell should be. Its not an every day tool, but its EXTREMELY valuable when your working on a project that has no source code available, just DLL's.
This is basically Task Manager on steriods. Gives you a wealth of knowledge about the Proc's running on your machine as well as the DLL's that are being used. It also can tell what folders/files the process is accessing. Really great tool made by SysInternals.
A few noteable tools i found on the list that I haven't used before but I will be sure to look into more:
This is a tool i've been meaning to checkout for awhile. It basically helps you to keep mutliple computers sync'd up. I can really use something like this to help keep my work laptop files backed up on my raid array.
Its apparently a virtual machine optimizer that can greatly reduce the file size of your virtual hard drives. I know recently this would have come into hand on a project where I was forced to use a 15+gig virtual and didn't have enough disk space to put it on my laptop (and my external hard drive had just died)
I've read about this tool and stumbled upon it before but never actually used it. It is a .NET library that lets you work with text files in a strongly typed manner. Its also FREE, which is a great price. I know a lot of times as developers we're forced to read in text files, so I think this library might come in handy on a project where your forced to use text files a great deal. It is certainly a tool I might try to make a small example on use about.
This sounds like a pretty cool tool. It is a floating command line utility which lets you easily open apps with just a few keystrokes. The real benefit here is that it helps to keep your hands on the keyboard and off that mouse!
I incourage you to check some of these out if you haven't already.