C related:

• MISRA, The Motor Industry Software Reliability Association. Interesting site with some freely downloadable papers (the C guidelines have to be paid for). Mission statement: To provide assistance to the automotive industry in the application and creation within vehicle systems of safe and reliable software
• Safer C by Les Hatton.
• How to Write Unmaintainable Code. Real fun. Shows you millions of ways how it should not be done.
• Dave Dyer's top ten ways to be screwed by C.

Other C/C++ Style resources:

• Chris Lott's resource pages.
• Indian Hill C Style. (One of the older and first documented styles)
• The MISRA C Guidelines. (A set of numbered C programming rules)
• NASA C Style Guide. (From NASA's Software Engineering Laboratories)
• FTS C Programming Style Guide.
• Shift-Right Technologies coding standard.
• Jack Ganssle's Firmware development standard. (Not really a C style guide but good development environment tips)
• http://www.literateprogramming.com/dssguide.pdf.
• Jean Labrosse's C coding standard.
• Paul Krzyzanowski's C Programming Style.
• Rob Pike's Notes on Programming in C.

Software Engineering:

• Embedded Systems Programming. Excellent website with lots of resources. Free subscription to the Embedded Systems Programming Magazine can be found here as well.
• Software Engineering Is Not Enough.
• NASA's Software Engineering Laboratory on-line Documents.
• Jack Ganssle's Embedded Systems Articles.

Open Source:

• Open Source Initiative OSI.
• GNU Library or Lesser General Public License (LGPL).
• Tip! Project Management & Hour tracking: Achievo

Version Control:

• CodeOrganizer list of Version Control tools.
• Tips: WinCVS, MicroSoft Visual SourceSafe and PVCS.

Software Testing:

• Software Testing Hotlist.
• Software QA and Testing FAQ's. Interesting listing, also includes a long list of historic software bugs and failures.
• A Collection of Historic Software Bugs.
• Software Horror Stories.