DreamingWriter, while I believe I understand your point of view, I disagree with it. This, again, all comes down to how self-interest is defined; it appears that we do not have an argument on what what motivates charity, but to what extent can we consider a charitable deed done in self-interest.
As Oniya above so aptly put, charity done with the intentions only of furthering one's personal goals is not really charity at all. That is one extreme. There are a plethora of shades of meaning in between, and then there is the other extreme. Jumping on a grenade, for example, seems completely selfless. I would like to propose a visual, Maslow's hierarchy of needs.
Let us assume that all self-interest must stem from those needs; I am using a definition of self interest that requires it be fuelled by something that one "needs". While the kind of charity that would be considered in self-interest would be on the fourth level, self-esteem, or the third level, family and belonging, it seems that the ultimate sacrifice (and sacrifices less ultimate) would not fit on the pyramid, especially if they are aimed towards people one does not know and one may not ever meet.
Again, allow me to emphasize to what extent do we consider the acts of charity falling under "self-interest". I tutor kids because I want to make friends with them, and because I derive pleasure from it. I would consider this fuelled by my need to belong. However, I also do it because I want them to grow, to be better, to make it past high school and into college. I do not know these kids very well, and once the year is up, I may never see them again. I do this because I want them to go out and make the world a better place, at least for themselves. My benefit derived from that is the improvement of humanity, but is the improvement of humanity really a benefit purely for myself? Is it really self-interest if I want everyone to prosper?