other angels/early investors:
Ram Shriram (angel)
Ron Conway (through Angel Investors LP)
David Cheriton (angel)
both Ram and David became billionaires (like Andy) from their angel investments so i'm assuming it was of the same magnitude ($100k ish) at around the same valuation (before kleiner and sequoia put in $25M at $100M pre)…
Mark Zuckerberg put in some money early on along with Eduardo. Also in the series A round (led by Peter Thiel) Mark Pincus and Reid Hoffman independently invested some money.
Greylock and Meritech invested in between Accel's investment and the DST investment.
Also Microsoft invested $240 million at $15 billion in October 2007.
– Union Square Ventures
– O’Reilly AlphaTech Ventures
– Jack Dorsey (Twitter (product) creator)
– Kevin Rose (Digg)
– Joshua Schachter (Delicious)
– Alex Rainert (Dodgeball)
– SV Angels / Ron Conway
– Chad Stoller (friend)
– Sergio Salvatore (friend)
See also: Who were the Odeo investors who were not interested in Twitter?
Bryce Roberts of OATV claims to be one of the "few others" that User mentions.
In the Series B, major investors included Peter Thiel, Matrix Partners, and North Bridge Venture Partners.
The Series C was led by Tiger Global, with existing investors also participating.
Hubert Burda Media, Allen & Co.
Wellington Partners and August Capital
According to http://www.krabois.com, Keith Rabois (business person) did.
Redpoint Ventures, Travis Kalanick, Baseline Ventures, Freestyle Capital, SV Angel, Floodgate,
Lowercase Capital, Chris Sacca, Dave Morin, Kevin Rose
Dogpatch Labs (not an investor but company was part of Dogpatch)