Hi,
If you are wanting to upgrade and keep the standard head unit there is not much point in spending a fortune on the speakers as the head unit won't have the power to run them to their full potential!!
If you aren't planning to change the head unit i would go for a set of pioneer components, but if you intend on changing your head unit I would go for some rainbows, bostons or focal's, that have a bit more ability!!
Hope that helps,
Phil