C #: How do you manage symbolic constants in your projects? Where do you declare solution scope constants?

It's quite rare (at least for me) that there is no explicit relationship between such constants and some pre-existing class, I would just add them there. The constants are then hard-coded to the relevant part of the model, rather than just being assigned to the "Constants" class.

Of course, I also very rarely manage to find true "constants"; many interesting "constants" are better described using configuration options.