This nest of the  malachite  sunbird Nectarinia famosa can be right in your face and it will still be invisible. We have two sunbirds on a regular basis in our garden in the Western Cape.  The  malachite sunbird with the male a glittering green all over and the smaller sunbird  Nectarinia violacea (also refered to as Anthobaphes violacea) where the male has a glittering red/orange breast. The females of both are little brown jobs. They love the nectar of the Aloe sp. and also the Cotyledon sp. I am not an expert in birds feel free to correct me if I am wrong.

The nest was exactly the height of my face right above the path. I do not know if the they hatched any chicks but the sunbirds must have spent a lot of  time building the nest  without us noticing them.
It is a pity that I do not have a camera with a zoom.  The birds will think nothing of sitting right next to us when we are in the garden, but we must not have anything in our hands.  I tried walking with the camera.  Fine, they got used to it, but the moment I lift it in their direction, they dash away.
There are more nests in the garden.  The juveniles resemble the females I guess we might have seen some without realizing they are "our" birds.
All birds are welcome in the garden and we see to it that they get some treats and water,  but we are not into birding as such.
---------------  I had to add this September 2009.
I found this little female sunbird  nesting on the other corner of the house.

The height of the nest above the ground is obvious by the window in the background - the white is the window pane, not the sky, with the reddish window sill at the bottom. The nest is slightly larger than a man's fist.  Now that I know about the nest I make a small detour around the tree, where I would normally pass directly against that branch.  It obviously did not bother the birds in building the nest, but I will do my share.

There are more nests in the garden.  The juveniles resemble the female I guess we might have seen some.
All birds are welcome in the garden and we see to it that they get some treats and water,  but we are not into birding as such