WMS Viewer on line is a light-weighted client for web map services that use the WMS protocol. It is a web application compatible with all modern versions of WMS and also supports
Saving map connection parameters and settings as links that may be bookmarked, shared or posted. Using these links your map may be displayed in any device at any time. See this post with examples.
Digitizing of points, lines or polygons and export in CSV or KML files
Projection of kml files as overlays in the displayed maps.
Projection of coastlines or country boundaries over the displayed maps.
It is a follow up of the Android application WMS Viewer and I like especially the fact that you can simply open it in a browser and just work with it. Most of the WMS viewers are heavy applications that require to be downloaded installed etc. You also may find it as an installable Chrome app in Chrome Web Store or as a native Firefox app in marketplace.