Original works of great mathematicians In almost every mathematical text there is a line as This was first proved by Gauss or This formula first appeared in a work of Riemann, but for me it's more like My friend told me once that...
For my Bachelor thesis and other papers I'm working on I would prefer to add a scan of the original paper rather that a quote from a book1 that quoted book2 that found it in a book3. I was already looking for some original papers from some great mathematicians (Riemann, Euler, Cantor, Hilbert etc...) on the internet, but I got quite disappointed by results. I expected some organization that collects scans from the old scientific works and makes them publicly available, but either I was looking elsewhere or it just doesn't exist...
So my question is:
Do you know about any place (website?) where scans of original work of great old mathematicians are collected?

Look, the scan of the first page of Riemann's original work Über die Anzahl der Primzahlen unter einer gegebenen Grösse !! Such a mathematical and historical gold...

 A: For Euler see the Euler Archive.
For many old books see the french Gallica
(the cited archive.org and gdz are great ressources too).
Don't forget google books and google scholar (for papers).
A list of important papers by wikipedia...
A: Try the European Cultural Heritage Online.  I used it to look at the original pages of Thomas Harriot's Artis Analyticae Praxis published in 1631.
A: Project Gutenberg is another potential source, although of the people mentioned above the only result I found was a book by Gauss:  General Investigations of Curved Surfaces of 1827 and 1825.
A: Here are some useful links I found over the years that haven't been listed here yet:


*

*Rare Book Room

*The University of Michigan Historical Mathematics Collection
A: I wonder if there are webpages yet to be discovered that collect collected works. If not it would be a great resource.
Here I stumbled on Weierstrass's complete works:
https://archive.org/details/mathematischewer03weieuoft
A: http://archive.org
Just search for "Bernhard Riemann", for example.
A: This is a useful aggregation site:
http://www.mathematik.uni-bielefeld.de/%7Erehmann/DML/dml_links.html
A: There are two books by E.T.Bell, (1) Men of Mathematics (2) Development of Mathematics.
The first one contains biographies of almost all great mathematicians from Archimedes to Henri Poincare, and contains wealth of information about their great works. The second book contains very unique and beautiful description about how mathematics evolved, right from numbers, plane geometry to modern branches like algebraic geometry. Every body interested in Mathematics would love to read these books.
