DANA SUTTON  The documentation doesn't say so, but this version is Tiger-friendly. The dialogue boxes have been changed so that it takes less steps to make an image file (one dialogue box less). So a great app. keeps getting better.  
(Version 1.2)

JIMW  There is a Widget available "Capture" that has a significant amount of this capability and it is free.  
(Version 1.2)

JOHN LITCHFIELD  A fantastic tool that rates an 11 on a scale of 10, BUT it hasn't been modified to work with Tiger, yet.  
(Version 1.1.6)

DANA SUTTON  I use ScreenShot Plus in my work all the time, it's a great utility, I panning this version only because when I try to launch it, all I can get is a "fail to encode" message and it crashes. Some folks are obviously having better luck, but the moral is that if you have a previous version installed, don't trash it until you are sure that this version works properly.  
(Version 1.1)

NCIANCA  Update - new version 1.0.6 now has a copy button to send the contents to the pasteboard.  
(Version 1.0.6)

NCIANCA  Looks pretty good, works as advertised. The only thing missing is the ability to send the image to the pasteboard rather then having to save it.  
(Version 1.0.3)