A nice WMS of the Canary Islands, GRAFCAN:

http://bbox.me/bbox.html?id=118

Apollo ERDAS elevation backdrop:

http://bbox.me/bbox.html?id=122

Shuttle RADAR DEM (http://www.opengis.uab.es)

http://bbox.me/bbox.html?id=123

Blue Marble NG (http://www.opengis.uab.es)

http://bbox.me/bbox.html?id=125

Night Lights (http://www.opengis.uab.es)

http://bbox.me/bbox.html?id=126

Here are som links to nice WMS bboxes:

http://bbox.me/bbox.html?id=108 (Globeexplorer data covering the entire globe).

http://bbox.me/bbox.html?id=109 (Great imagery of Mecklenburg)

http://bbox.me/bbox.html?id=105 (Imagery of Prague)