how to gracefully degrade when the cache is down?

We've been adding a lot of caching lately to speed up our reads, and it's working great! But I was thinking about what happens when the cache layer itself has an issue, or becomes unavailable. Ideally, we don't want the whole application to just stop working. What have you all found effective for gracefully degrading service when the cache is down? Are there common patterns for this, or is it mostly application-specific stuff?