A short list of active contributors to Bitcoin, ordered by first name.
Andreas Schildbach (Profile) - original developer of Bitcoin Wallet for Android (Google Code Project).
Amir Taaki (Wikipedia) aka genjix- creator of the BIP process, Libbitcoin C++ developer toolkit, Obelisk blockchain server (later BS), SX bitcoin command line tool (later BX), Darkwallet, Darkmarket (later OpenBazaar), Darkleaks, Freecoin and well as inactive/defunct projects such as the Britcoin exchange, Intersango exchange, Spesmilo RPC client, Bitcoin Consultancy, Bitcoin Media Blog (author), Vibanko web wallet provider, GLBSE exchange client, Kartludox Bitcoin poker client, Pastecoin and Python bindings for Bitcoin.
Art Forz- developed the first GPU miner and at one time his GPU mining farm (the ArtFarm) was mining over a third of all blocks.
Gary Rowe (Profile ) - Contributor to the MultiBit (http://multibit.org) and BitCoinJ (http://code.google.com/p/bitcoinj/) projects. Working on various Bitcoin based businesses.
Gavin Andresen - (Profile ) Former Satoshi client maintainer. He previously worked at Silicon Graphics and now runs his own company.
Hal Finney- one of the creators of PGP and one of the earliest contributors to the Bitcoin project. First to identify a type of double-spending attack that now bears his name -- the Finney attack.
James McCarthy aka Nefario- creator of the first bitcoin stock exchange GLBSE
Jed McCaleb, original developer of MtGox. Previously created eDonkey2000.
Jeff Garzik- (Wikipedia) Satoshi client core developer, GPU poold software and the founder of Bitcoin Watch. Works for BitPay.
Luke Dashjr aka Luke-Jr- Eligius founder, maintains BFGMiner and maintainer of bitcoind/Bitcoin-Qt stable branches.
Mark Karpeles (Wikipedia) aka MagicalTux- Former owner of MtGox and this wiki.
Martti Malmi aka Sirius- Former Bitcoin developer. Operates the domain names bitcoin.org and bitcointalk.org.
Matt Corallo aka BlueMatt- Satoshi client and Bitcoinj developer.
Michael Hendrix aka mndrix- creator of the now defunct CoinPal and CoinCard services
Michael Marquardt aka theymos- creator of the widely used blockexplorer.com site, and BitcoinTalk Forum
Mike Hearn (Profile) Google engineer who works on Gmail and developed BitCoinJ (http://code.google.com/p/bitcoinj/) and Lighthouse.
Nils Schneider aka tcatm - Bitcoin developer, owner of BitcoinWatch, creator and owner of BitcoinCharts, GPU mining software and JS web interface.
Patrick McFarland aka Diablo-D3 - DiabloMiner author, and former BitcoinTalk forum moderator.
Patrick Strateman aka phantomcircuit - Bitcoin developer, creator of Intersango, member of Bitcoin Consultancy and creator of Python Bitcoin implementation.
Peter Todd - Bitcoin developer. Involved with Bitcoin related startup Coinkite and DarkWallet.
Pieter Wuille aka sipa- Satoshi client developer and maintainer of the network graphs http://bitcoin.sipa.be
Stefan Thomas aka justmoon- creator of the WeUseCoins.com site/video and WebCoin.
Tamas Blummer aka grau - author of Bits of Proof, the enterprise-ready implementation of the Bitcoin protocol. http://bitsofproof.com
Vladimir Marchenko- (Profile), runs Marchenko Ltd which sells mining contracts, previously developed the figator.org search engine.
Wladimir J. van der Laan - Satoshi client maintainer.