As an undergrad Engineering student, there are two resources that have come to my aid leaps-and-bounds above other resources. Google, while not included in my list, is a given but the other two have seemed extremely obvious after I've mentioned them to people.
Some of the courses on the Engineering tract, at least with UF, include Calculus 1-3, Chemistry 1 and 2, and Physics 1 and 2. While I haven't begun taking my physics classes yet, the first resource has been extremely helpful with both Chemistry and Calculus. That resource is Wolfram Alpha. When Wolfram Alpha first came out, it felt like the population collectively said "that's neat," and then moved on about their day. At first I was blown away by the wealth of data they had amassed and how it could be mashed up on the spot. But alas, after a few hours, I too felt the same way.
As someone who had regularly used the functions built into Google search (such as the calculator, dictionary, unit conversions, etc), Wolfram Alpha expanded that ability ten-fold. It wasn't until I thought to try plugging in an equation in my Calculus class that I truly grasped how powerful the site was. Low-and-behold, not only did it solve the problem for me, but it provided a detailed step-by-step guide as to how it arrived at that answer. It also provided the Calculus identities that we Engineering students oh-so-often forget in our calculations, as well as numerous other metrics about that particular equation. I was blown away. Calculus was much easier to grasp after that, not because it was solving equations for me, but because I could see exactly how a question was to be approached. It felt like I had my own professor around to tutor me whenever I needed it.
Chemistry has been the same way. I've been able to plug in practically any element or compound and glean whatever data I need about it. Being able to naturally ask for metrics about particular elements or equations has been particularly power as well. For example, plugging in "What are the isotopes of Carbon?" yields the three main isotopes that Carbon can be found in. From that information you can then go on to calculate the atomic weight of Carbon (or, you know... simply plug in "What is the atomic weight of carbon?") or gather any other data about it that may be of use.
The second resource that I've used has been more helpful for my Mathematics courses, particularly Calculus. This is also the resource that people facepalm themselves for not realizing after I mention it. Youtube.com is that resource. One might say "Wait wait, how are videos of kittens riding Roomba's going to help me?" Fear not, my friend, for mathematics teachers love to record themselves doing lectures on how to perform almost every type of major mathematics skill. And for this, we thank them. I've been able to look up almost every permutation of Calculus concepts online and find a lecture or instructional video directed at that concept. Once again, I've essentially found a way of providing myself a virtual instructor for when I'm not in class. This resource has been so helpful in fact that when I've had a teacher that was, for lack of a better word, horrible, I've been able to relax knowing that I'll find some decent instructional videos on Youtube. My current Chemistry teacher is a great example of this scenario...
So, while these sites may not be very eye opening (OK, they aren't, I know), you'll be amazed how much you can accomplish with their help. If you're struggling in any technical courses I recommend checking them out to see what they can offer. Especially with Wolfram Alpha, just type in some important keywords about a concept and see what it throws out at you.