In my previous job, I use SnagIt v8.x in creating screenshots and I would say that it's a great tool. It's very efficient, non-obstructive and relatively lightweight screen capture tool. I find it an indispensable tool especially when doing documentations or user manuals and also in creating screenshots for blogs. However, SnagIt is not free. So below are some of the screen capture I use in place of SnagIt.
From the creator of SnagIt, TechSmith, comes Jing Project is simply Jing. It has the same basic capabilities with SnagIt but is primarily targets online sharing whereas SnagIt is more directed towards professional documentation. I used the free version for quite some time until all 'non-standard software installs' were asked to be removed in the office.
It's a completely free lightweight screen capture tool. It's so easy to install(just extract the package) as long as you have the dotnet framework installed (most likely already pre-installed because it's used by a ton of other programs, even comes with MS Office).
I moved to this tool after Jing because it's free. Greenshot is not a shareware and doesn't require you to fill out registration forms. Not having to 'install' it also adds to its advantage because I just need to extract the package. :)
Other than these two, there are literally hundreds of others out there to choose from. I even used Snippy, a very simple screen capture that directly outputs to file. Unfortunately, it's overly simplistic it needs several steps to capture and paste it to a document.
This is the one I'm currently using on my netbook. It's far from the Windows counterpart but is usable. I find it slow and tends to hog memory. However, I'll continue to use it until I find a suitable replacement.