If you’ve tried the previous tip but have a tool selected that also has blend modes associated with it (like any of the Brush tools), then you’ll find that the keyboard shortcut cycles through the blend modes for the brush in the Options Bar and not the layer.  The workaround is this: First select a tool that doesn’t have blend modes (like the Move tool or one of the selection tools), and then use the shortcut from above and it’ll work just fine.