Web applications backed by Pylons

(installable by users)

SFLvault - A networked credentials store and authentication manager. Great to maintain a large park of servers, switches, routers and other machines (has a CLI client for the unix geek).
Adjector - A fast, slim, flexible ad server

Web sites backed by Pylons

27Jobs - Search Thousands of real jobs.
3aims Web Development
AdRoll - Simple, effective display advertising for brands of all sizes.
Ain't Just Soul - Let's you listen to records on eBay.
Arcadia and Ricono - Italian literary agency. Site is backed by a lightweight, i18n-enabled CMS built on Pylons 0.9.6.1 using elixir for modelling, babel for i18n and mako for templates.
A Swift Half - UK pub searching and reviews.
AuthKit
Automotive News Ecommerce
Bel-EPA - personal site of Graham Higgins, uses Pylons with a native XML database (eXist) and semantic web RDF (rdflib).
BitTorrent - (yes that BitTorrent)
BlackLedger Resident Clubs - Offers discounts to residents of apartment communities.
Blockparty NYC - Allows users in NYC to add and find blockparties taking place in their neighborhoods.
byCycle.org - allows users to find the best bike routes in a couple select cities (so far)
http://btbytes.com - personal site of Pradeep Gowda. Uses pylons with docutils,Mako on a NGINX server
Car.gr - Largest online car classifieds website in Greece.
Clinical Indications - In conjunction with NHS Innovations South East
Charlie Rose - Website for the popular PBS Show.
CMS - Water and environmental conference and event organisation.
CLS Legal Staffing - Chicago-based Paralegal and Legal Staff recruiting site with job listings. Runs on a custom made CMS built on Pylons with Elixir, AuthKit, jQuery, Mako, memcached, and table-free CSS layout.
Codepad - A pastebin that runs code in a variety of languages (including Python, of course)
CSM Worldwide - International Automotive Consultancy, i18n multilingual site, full content management system, e-commerce, event registration, document management system
Deal Sharing Community Network - Share deals, discount, freebies and Garage sale information on Internet. currently in development stage
debexpo - Debian package repository used for mentors.debian.net
ddportfolio - Debian Developer Portfolio Service uses Pylons, jQuery and Formencode to build Debian Developer related URLs
debshots (screenshots.debian.net) - storing screenshots of Debian applications with a spice of jQuery
Developer Community (Ukranian) - Russian/Ukranian web portal for developers.
Driverfall - World's biggest driver resource, currently in test drive
Entic.net - VPS server/Pylons hosting - Get up to 50% off just for Pylons developers - email us!
Fanfeedr.com - Sports and social networking.
FreeLDAP.org - a free LDAP service for address books and more
FireEye, Inc.
FormBuild
Fotobuch-XXL
Foxmarks
freebase - a open database of the world's knowledge, currently in beta
Gainlog - Work organizing and project management tool based on Pylons and SQLAlchemy
General Sports & Entertainment - The power of sports and entertainment
Gazest - Pylons powered wiki application (demo site)
Idée Labs - Idee's technology showcase, focusing on visual search. Front-end is powered by Pylons.
iDesk - an application to collect and share informations easily
IM Feeds - Delivers RSS/ Atom updates to your instant messenger
IncidentNews - Information on current and historic oil spills/hazardous material spills in US waters, by NOAA's Emergency Response Division (US government site)
indiconews - Citizen journalism website, recently rewritten from php to pylons/sqlalchemy. Facebook app for this is also part of the pylons project.
JeugdKosk - Youth section (in Dutch) of the Chess Club of Ostend (Belgium).
Jingobid - An auction website which allows people to win high quality electronics in English and Cantonese.
koitank - A koi (japanese fish) management software for a web shop.
Lab Engine - Project management/ bioinformatics software for researchers.
LosoweHaslo - A simple random password generator with a Polish interface
Lunartics - Meet the Universe's most quirky and colourful oddballs!
MadForIT
Market Shares Australia - In-depth current and historic stock market analysis and portfolio management for the Australian stock market
Matisse & Jack's - Natural foods online store for Matisse & Jack's products
Mudanças - Transportation and Changes.
Melkjug - Tunable open source RSS news reader
Mudanças - Changes home.
MochiAds - Ad network for Flash games
Octopart - Search engine for electronic parts.
Odosh - Personal type and relations harmony detector based on computer vision
PDFTextOnline - PDF Text Extraction in Your Browser
Parachute
Popego - Know your (Digital) self.
PrideLife - A website which accompanies the UK based pridelife magazine. Fully developed with Pylons including a custom made CMS.
Pump Pro Edits - Edit step files for the arcade game Pump it Up Pro
PylonsHQ - This website
Project HQ - An open source project management system. The site runs Drupal, but the app itself is written in Pylons (see the online demo of the project).
Random Idea - Webdesign and development portfolio site showcasing the talents of Random Idea
Reddit - a collaborative news site(announcement)
RUProm.net - Russian B2B marketplace
Sauce Labs - Selenium-based cross-brower testing cloud service, open source software, and support.
Freelancing projects - Locate and search freelanced projects
Faltzer's HQ - A blog where web development and general programming take place, and is home to a few Python web apps. This site runs on the Pylons-backed mini-blog application, Scribo
Snowtide Informatics Systems, Inc.
TRTF - The Russian Technology Fund (venture capital investment opportunities in Russia)
The Microshare Project - Pylons XUL demo
This One Next - Book, music and film recommendations
Toostis - Events you care about.
Transportadoras - transportation of containers.
TradeVibes - A platform for sharing, discussing, and evaluating information about new startup companies.
Trimet is using Pylons for internal projects (there are plans to release some of this code at some point).
Tvnext.si - Calendar with TV series release dates
TweepTracker - A web app to manage twitter followers,friends, and whatnot.
Two Peas In A Bucket - The internet's #1 online scrapbooking retailer and community. They're migrating the entire site from Classic ASP to Pylons.
UAProm.net - Ukrainian B2B marketplace
UrlZip.fr - TinyUrl Like
URM Exercise class distribution and management at a University in Germany. Students register with their preferences for the classes and get distributed in an optimal fashion. Site is in German.
Virgin Charter - Marketplace for private jet charter
Virtual Teams: Howto for Software Developers - Online book for virtual teams of developers
We Give app on Facebook - Send digital gifts to friends and raise micro-donations for small, passionate charities
What Should I Read Next? - Book recommendations
WisdomTap - Product search and recommendations
Walter Cruz - Artigos
Webhosting.pl - Polish, portal about internet technology
ySage - Investor insight into listed companies (US now, more countries coming soon)
VestDanmark - Danish holiday and vacation-house portal.
Siafoo - The intersection of pastebin, help desk, version control, and social networking

Links Entered Out Of Order (Perhaps for a Reason?)
Jaworznicki Portal Społecznościowy - Polish, local portal for city Jaworzno.
Pure Expressions Photography - Photography studio
MyLanck.net - Russian Internet Service Provider Portal for Clients. Including forum fully written with Pylons.

Links not currently working:
Blackberry Tracker Pylons site that enables you to track GPS-enabled Blackberry Phones.
Cheeseboard - A Cheeseshop mirroring system (10/14/2007)
IMDBTube - All IMDB records and related YouTube videos, currently in development (8/11/2008)
Joblint - Software job board

Probably spam:
Veekun - Veekun