1. Begonia 'Escargot'
2. Begonia species (have that at home, name follows tomorrow)
3. ... rhizomatus cultivar
4. Begonia masoniana 'Iron Cross'

2. Begonia cardiocarpa
At least I received the cutting labelled as this species.
It does not look identical to the pictures available at absastro.tripod.com, but this could be due to light differences.
My plant's red parts become more intensely coloured if the illumination increases.
I sent the links to your pictures of Begonia Nr. 2 to a nursery specialised in Begonias for further investigation.

i don't think #2 is B. cardiocarpa. this is most likely a B. ricinifolia cultivar. If you'll notice, B. manicata also has rings of red hairs, so you can't really go by just that character.

4. should be B. masoniana, "Iron Cross" (single quotes denote a cultivar, but this is a true species with a common name).

-ming