Oleg Kiselyov
His "home page" at http://okmij.org/ftp/ is a tremendously valuable collection of code, papers and archived UseNet posts on the HaskellLanguage, on the SchemeLanguage and Macros (he shows "How to write seemingly unhygienic and referentially opaque macros with syntax-rules", i.e. he writes unhygienic macros using the hygienic DefineSyntax macro system), OnMonads, on types and type systems (see TypeArithmeticsPaper), on LambdaCalculus and ChurchNumerals etc. Then there's the specification of SXML (an embedding of XML data into Scheme), a scheme implementation of a PurelyFunctionalObjectOrientedSystem?, CeePlusPlus libraries for numerical mathematics and image processing etc.