What is the easiest way to memorize big amounts of information (a.k.a. learning for exams)? I consider myself a person with above average intelligence, that is, I am able to understand complex systems with relative ease. My weak point however is that I've always struggled with memorizing. Back in school I excelled in math and physics, but struggled with e.g. history, not because I wasn't interested in it, but simply because I had a hard time memorizing what was necessary.

Is there a good method for memorizing? 

Context: I am planning to go back to university this fall. I am learning now for the entrance exam. That is something I will manage, but I anticipate university exams themselves being harder than that, and I will attend to uni while still having a day job. That is, I have no time to waste on improper/suboptimal learning methods. I aim for BA first, then MA. I am 31 years old now.
If you want to learn something then investigating how the brain encodes memory, and looking at methods of enhancing these tasks is the way to go. Pop psychology books do the field little credit and are often riddled with academic inaccuracies. However if you are going to use a book I highly recommend Human Memory by the brilliant Alan Braddeley.

Memory is largely split between three according Atkinson and Schiffrin's (1986) model: sensory store->short term store(STM)-> long term store (LTM). Although this can then be sub-split into explicit and implicit memory, and the sensory store is what we would now call attentional processing. Broadly speaking we have little control of attentional processes than STM. So lets look at how you many enhance the encoding between STM and LTM. Much of what I'm about to mention comes developed out of the Levels of Encoding theory which essentially suggests that information is processed at different levels depending upon the complexity and relationships, the greater the depth of the encoding and associations the easier something is to remember. Many Mnemonic (memory) techniques are based on this. For instance, "Richard Of York Gave Battle In Vain"= the colours of the rainbow. technically this is shallow encoding because its only the first letter or each word relating to the colour in the order they occur in light refraction. But this is are easier than remember the colours based upon there discrete and unconnected names. The more associations you make the easier something is to remember as it makes more associations heres an deeper example remember this list and hide it once you have read it and try to recall after the maths test: Carrot, Monkey, Telephone, Guitar, School, Bottle, Newspaper, Mansion, Henry, Catastrophe, Worms, canopy, Hairspray. 

Answer the following: 2x3.5=?, (7/2)x3=?, square root of 27?, A car accretes from 0-50 m/sec in over a distance of 34 meters how long did it take? 

Recall the list?  

If instead you tried to recall the list as a story it would be easier to remember all the items...

A Monkey was eating a Carrot when the Selephone rang offering Guitar lessons at a School, he/she decided to go and packed a Bottle and Newspaper. Upon leaving the Mansion he/she walked past Henry who was having a Catastrophically collecting worms under his fishing Canopy with a Hairspray can.

This is a deeper level of encoding that should be easier to remember because it has more detail applying the words in an episodic and semantic style. This activates more brain regions providing more cues for how associations for the information that one wishes to store. I literally can't write enough about neural encoding of memory there is a plethora of research, and I strongly suggest a google scholar search if you are interested. But the over riding suggestion is increase associations, for instance when I was studying for my exams I would write notes and cue cards which were highlighted, I would also create stories and words made of the items I wanted to remember. In addition I would drink a particular flavour of squash while doing my learning and revising. The reason being is that these all create associations, and if you can take a cue with you into an exam, such as apple juice, it well help you to remember. Visualisation a lot too, imagining the place you were when you learnt something and the smells and related tastes.

Finally it cannot be understated the role that affective (emotional) processing plays, information is often affectively encoded. Trying to remember how you felt or giving data affective significance can aid recall or being in the same state of affect helps.

Essentially a large part of memory can be understood in terms of Pavolivan and operant conditioning, coupled with motivational and affective relevance. In other words learnt associations and reinforcement may act as cues and learning mechanisms that strengthen memory. The relevance of these cues one can give both motivational and affective significance, and these may also be used to help recall. In addition the level of detail and information relative to the encoding process strengthens or deepens the learning process. 

This is a REDUCTIONIST explanation of memory there is a lot more on it and the precise mechanisms related to what is being learnt, there is also a lot i haven't mentioned. Sorry for the lack of references I have a job to do, but you can google a lot of these topics and you will encounter most while learning about cognitive neuroscience. Memory research is probably one of the best understood areas of cognitive neuroscience along with perception.