What, if anything, should you offer as a reward to your early adopters and to those who support your startup through seed investing, Series A, investing, and the like?  

I know that some founders offer big donors a stake in the company, but I've not felt comfortable turning that much control over.  As such, I've stuck to smaller rewards.  You could always offer a lifetime of free updates, if you've created an app.  Additional options are to offer free merchandise or access to behind the scenes material.