Screenshots can show your clients exactly what you mean in a particular context. Here are five apps that act as extensions of the basic screen capture system.
For those interested in a comprehensive package, SnagIt by TechSmith is one of the bigger names in screenshot and video recording apps. In addition to offering multiple modes of capture (i.e. full screen, window, region, et al), images and videos that you create are automatically saved in an organized and catalogued fashion for quick retrieval. Basic editing capabilities exist as well, allowing for quick crops, drawing lines and shapes and countless other effects. SnagIt can be acquired for $49.95.
TechSmith also has a little brother to SnagIt in the form of Jing. Although much more simplified in terms of features and capabilities, the app is free to download and use. Essentially, you have most of the same image and video capture functionality with a subset of the editing tools that typically come with SnagIt. It even includes a similar control-panel "bubble" which can be dragged around for easy access to the Jing.
If you need to create an on-screen video recording versus simple screenshots, CamStudio is a worthy candidate for the job. The user interface simply stays out of your way and you can create projects ranging from tutorial videos to product demos and distribute them as AVI or SWF format files. As a nice bonus, CamStudio offers a free lossless video codec which is also rather efficient on bitrate, while providing a quality video, devoid of artifacts and chunking.
Combining an elegant user interface with the ability to quickly push screenshots and video recordings to the cloud seems to be the forte of MangoApps, creator of Tiny Take. I find TinyTake to be similar to SnagIt in its image editing and annotation tools, all with a price tag of $0. The only minor annoyance I've noticed is that, in order to properly use TinyTake, you need to create an account using a "business" email account, ala no personal Gmail, Live or Yahoo! email. Fortunately, I was able to mitigate this concern, using another personal email address that is attached to a custom domain name.
For the open source enthusiasts out there, you haven't been forgotten either. Greenshot is a screenshot utility for Windows provided under the GPL. It takes images and handles edits with aplomb. There are also plugins that offer integration with Atlassian's JIRA and Confluence, making quick snaps and uploads to a wiki page painless.