If you have the free time or getting bored with Year 10 maths, I'd probably recommend taking a look at those olympiad type maths problems. Things like
http://www.mathscomp.ms.unimelb.edu.au/pastsol.php or
http://www.artofproblemsolving.com/Wiki/index.php/IMO_Problems_and_Solutions Actually that Art of Problem Solving website is fairly good, I don't know about the actual books because I've never seen them, but the forums (and wiki) there have a lot of interesting stuff
http://www.artofproblemsolving.com/Forum/index.php You'd probably be looking at those 3 high school sections there.
If you see a problem that you think you can do, try it out. Do some googling if you have any questions that arise from trying to solve them. If the problem turns out to need stuff you haven't learnt, then go read up on that stuff. Rinse, repeat etc.
It won't really help prepare you for VCE exams, but it'll be a lot more interesting.
There's also a lot of interesting maths books, at various levels, that you might find in a library (if you live near a uni, go take a look) or via other means. Some unis have some kind of borrowers scheme for secondary school students (such as
http://www.deakin.edu.au/library/join/#schools), and fairly sure all of them will have something or rather for public access (but that might be attached with a fairly hefty fee).
I've read some of the books in this series
http://www.maa.org/ebooks/nml.html and they're fairly interesting. You'll want to google the name of the book and take a look at the preview pages on Google Books, Amazon or whatever and see if it looks interesting enough to read.
archive.org also has a fair bit of stuff. These books here are pretty good
http://archive.org/search.php?query=creator%3A%22Yakov+Perelman%22 I'd recommend taking a look at Algebra can be Fun from that selection. If you come across the djvu file format, use SumatraPDF or another djvu reader to view them (on windows anyway,
http://blog.kowalczyk.info/software/sumatrapdf/free-pdf-reader.html)