The quintessential blog for the cool things people have made. If you're thinking of starting a project, its not a bad idea to scan through Hack a Day to see what other people have done similarly.
- Make Magazine
Do it yourself TO THE EXTREME. These guys are the forerunners of the new national do-it-yourself movement, and strong proponents of hackerspaces and makerspaces nationwide.
A great place to go for DIY projects with really good explanations.
- IEEE Automatons
A robotics blog with ties to the defense, commercial, and recreational industry. These guys tend to report on all kinds of mechatronic developments.
A blog dedicated to robots and cool inventions. They have tons of fun stuff all the time, and are worth a check every month or so.*Online Education*
- Let's Make Robots
A fun, interactive community of people who post their hobby robots and how they made them. This project was started by the guy who made the Little Yellow Drum Machine, one of my favorite hobby robots ever (http://www.youtube.com/watch?v=_RyodnisVvU).
The Kinematic Models for Design Digital Library, hosted by Cornell. These are basically the coolest kinematic models you'll ever seen, most of which were built between 1850 and 1925 (when mechanical engieners and machinists were Badass Heroes You Don't Fuck With). Any motion you could possibly want to make can be derived from the mechanisms buried here.
- Technology Student
You have to forgive the website, but this site contains everything you could possibly need to know to restore mechanical engineering and design as a profession if the apocalypse hit. Come, be prepared to withstand harsh graphics, and learn tons of stuff.
- Machine Design
A free trade magazine that offers monthly tips on design practices, spotlights on new mechanical designs, etc. etc. To be honest, I got it for the advertisements - this is the primary venue for new mechanical engineering products to be advertised, so if you ever wanted to know what's the newest development in real mechanical design, you get this magazine. That being said... I've been trying to stop receiving magazines for the past two years, and I haven't gotten them to cease and desist yet. So decide now if you want to receive a mechanical design magazine FOR THE REST OF YOUR NATURAL LIFE.
- How Stuff Works
As corny as it is, I learned most of my initial foundation of mechanical engineering knowledge by reading How Stuff Works. They tend to have really well-thought out articles that, while not necessarily deep, are certainly good broad overviews.
General Knowledge, etc
- This Old House
I would be completely remiss if I didn't mention This Old House. Go get your home improvement on something fierce.
- Open Courseware
MIT is on a mission to publish as many of its courses as possible, and the result is Open Courseware. If you ever wanted to learn basic physics (or quantum physics, for that matter), check out their online syllabis and projects. I suggest attempting this with a friend, however, as it's super easy to just drop online courses like this without continuing motivation.