Excel 2007 includes this capability. Create the chart, then right-click the axis and select Format Axis... | Axis Options tab. Check on the 'Logarithmic scale' checkbox and set the minimum, maximum, and major unit values as desired.
For earlier versions of Excel, follow the steps in the tutorial below.
Downloadable PDF file (flexible-log-scale.pdf) (requires Adobe Acrobat)
Downloadable help file (flexible-log-scale.chm)
Keywords: log scale, any values on axis, axes, non default gridline
