Thanks for the comments.
I probably should have put captions on them.
For the first one, I tried to frame the leaf the spider was on. Perhaps that was a mistake.
The second one is actually a stink bug (a type of shield bug). These are the nasty ones that eat bits of orange plants and spray you with really pungent liquid if you piss them off.
As Biggzie says, the third one is a jumping spider. If you look carefully it has half an ant in its mouth. A white-tail spider looks like this:
The fourth is a small
Argiope sp. spider, probably a St. Andrew's Cross spider.