PromptPal. It's a great enhancement for the standard Windows command-line utility. It adds stuff like tabs, favorites, command-completion, and a help-panel that shows you a command's syntax as you're typing it. I don't much like the "split screen" view that appears in a bunch of the screenshots, but you can shut that off.
FileBoss. While I don't use this too often, as I've yet to find an Explorer replacement that correctly handles Windows shell extensions like Carbonite Backup, it's great if you need to do something really weird to a large group of files, like converting all spaces to underscores or something like that.
DeepTrawl (I got a free one for sending a couple of bug reports). Yeah, there are a bunch of websites (and most HTML editors for that matter) that'll validate your HTML for you. This gizmo does a better job than all of 'em. In addition to pointing out HTML errors, it makes suggestions for things like your search-engine-bait meta tags and such.
Interestingly, DeepTrawl is written in Java. That means that for the first time in about two years (when I did a software project using Eclipse), I have a standalone Java app on my machine. Just thought it was ironic, given that ten years after Sun's proclamation that by now I'd be running nothing but Java apps on a Java OS on a computer that ran Java instructions in hardware, I have exactly ONE Java app on my machine.