If they all go to same GL account/fund then that's not an option. I'd suggest the gift subtype. It's a table field on each gift record so entry would be consistent, can be used for query.

Continuing this string, I agree that you shouldn't use the Appeal field to track online gifts, since Appeal really should be how they were solicited for their gift (membership renewal, direct mail, etc.) I'd like to know how many of you use Gift Subtype and Gift Attributes to track your online...