my vote goes to ItextSharp.
it’s a port of the iText open source java library written entirely in C# for the .NET platform. iText# is a library that allows you to generate PDF files on the fly. It is implemented as an assembly.
http://itextsharp.sourceforge.net/
its really amazing. you can create pdfs on the fly, add digital signatures, …
cheers, Andy
novastar22 at yahoo dot de
@Ayende and @Frans
Frans is right about that project owned by a company are stablished now and dont need the money or that must be provided by theirs companies.
ie MONO will dont go slower or faster if they get 2500 more bucks, I think that Jeff want to help comunity driven projects that are “OWNED” by the community.
BTW, some comments suggest soft that is not open source like TDD.NET or Lutz Roeder is clear for the article that them dont qualify
Cheers
I think Bill Gates made $10,000 in the time it look for this webpage to load.
I think we should consider smaller projects where this could help, not large projects that already have money via corporate sponsorship (like mono) or commercial support (like dotnetnuke I assume).
Actually I think a better idea is to give the money to specific tasks like google summer of code. Just donate the money to the SoC project even. Or propose .NET coding projects on rentacoder.com. You could get a whole new .NET-based operating system developed there for about tree-fitty, I believe.
Amen gemils!
SourceSafe is such a burden.
Subversion++ (I know it’s not .Net. Give me some money an I’ll port it to .NET ) 
I second MbUnit and raise you the whole Castle project.
Open source doesn’t need money to become solid, it needs attention. Just throwing money at open source is what MS is doing for years and it hasn’t payed off. The reason for that is that the mentality of the average developer on MS platforms is that you simply pay for controls, libraries and tools and if you work on these products, you get payed.
You won’t hear me complain about that mentality, as an owner of an ISV which targets .NET, I like that mentality from a business POV and with me all the other ISV’s which do the same: target .NET. 
For open source, that mentality isn’t that great: less people are interested in devoting large piles of time to a project and when it’s released, the majority of developers often won’t even think about looking for an OSS alternative to commercial offerings.
THATs what’s lacking in the MS’ ecosystem for open source. You can throw money at it, but that mentality won’t change. One of the core reasons it won’t change is because MS won’t let it be changed: if it does change, their days are numbered.
CMS using ASP .Net, VB .Net and SQL server.
Simple yet flexible.
Very interesting read … I hadn’t heard of almost any of these projects except for Paint.NET and NUnit. In particular, NGenerics looks very intriguing, and the license is compatible with Paint.NET’s so I might find a way to use it.
I’ve tried to make a point of supporting the projects that help me out on Paint.NET. I’ve sent cash over to projects like famfamfam.com (EXCELLENT and FREE icon libraries) and Window Clippings by Kenny Kerr (http://weblogs.asp.net/kennykerr). Embarassingly I have not yet contributed to #ZipLib, which is an excellent library and is at the heart of the Paint.NET auto-updater. I was going to help out the TortoiseCVS guys with some 64-bit hardware because it didn’t work on XP or Vista x64 at that time, but they managed to figure things out anyway (yes, I use CVS, and yes apparently according to Linus Torvalds that makes me “ugly and stupid” :)).
P.S. Thanks to everyone who’s mentioned Paint.NET
-Rick (the Paint.NET guy)
I nominate the Commerce Starter Kit (CSK) - http://www.commercestarterkit.org - it’s a well thought out, well constructed, versatile and generally excellent platform for commercial endeavours. It’s one of the few pieces of open source software I know of that can help generate income rather than simply supporting the development process itself.
Well, you’re right that you can’t easily block the ad.
But, that begs the question - is preventing the ad-blocking a smart thing to do? I rarely click on ads (as I block most), but I certainly won’t click on ads that prevent me from blocking them.
ScrewTurn ( http://www.screwturn.eu )
Best wiki ever met for small to mid-size wikis.
Best regards,
Joanns
http://www.lokad.com
I vote for Paint.NET which is just sweet, and if I can make a self-nomination, for ScrewTurn Wiki (http://www.screwturn.eu).
+1 for paint.net. Greatest program ever.
nlog - http://www.nlog-project.org/
A late entry for new, up and coming:
A web-based IDE for distributed programming using IronPython
http://softwareindustrialization.com/AWebbasedIDEForDistributedProgrammingUsingIronPython.aspx
Also, it would be nice to get .netTiers out of codesmith. - http://www.nettiers.com/
Add a vote for Paint.NET from me to the list if you’d be so good
I’d like to throw Paint.NET in the ring, as well. It seems to be quite well represented, but hey - it’s good. Between the UI, the user developed plugin support, a vibrant forum…it’s definitely revolutionary. Easy to use, moderately powerful. Paint.NET is fantastic.
Paint.NET for the win 
I’ve been using this application for quite some time now, and i have achieved lots of nice works! (find them on my dA account!) It has a great UI, a very supportive community, and ofcourse, the ability to create and share plugins, which i use even more then the included effects.
I nominate Robert Simpson’s System.Data.SQLite which is an ADO.NET 2.0 provider for SQLite.