I see no subjects in your sig!
Regardless, I'd recommend Checkpoints (and any further questions-based books if required) for any Science/Maths subjects. TheMethods 3/4 Checkpoints book is quite useful - it covers most SAC-type questions you're likely to get, and lets you see the thought processes required to answer them.
Don't spend too much money on anything English. If your teacher is good, just ask them for guidance with regards to your writing. If your teacher is crap, maybe get one reference book (the essay skills one that was recommended earlier?) or something if you're really desperate and invest in a tutor whilst you're at it. If you're really itching to do something, find out what your 3/4 texts are and read them ahead of time.
No matter what you do though, remember that the key to success is work. It's all and well to buy VCE-help books, but unless you actually use them properly, you're just wasting money. Especially with English, again as mentioned earlier, you should be writing as much as possible whilst you still can. ^_^