I think that the current three choices "proposal" "photo" "WealthPoint profile" don't encompass enough possibilities of the types of attachments we all might want post. I'm thinking that there are a lot more choices needed. For example, "profile" could be broader -- to encompass wealthpoint, foundation directory online, or other products. Or you should make it more specific, by adding "FDO Profile" as a choice to complement "WealthPoint Profile" since WealthPoint works for individuals and FDO works for organizations.
Also, you might want to add the "RFP" type. For example, I've got an RFP from AARP Foundation that I'd like to attach to their record...
You can add whatever you want. This field is populated by a Table in RE Config in your database. I just double-checked. You can't (yet) add a value to the table from NXT, but you see all options from 7, including table entries marked Inactive. (Which I hope won't always be the case! I don't want to see or be able to choose and Inactive value for anything.)