GTX 560 TI temperatures? (safe)

No. it should work fine. It's operating within it's design parameters.

Would it be worth investing in a better cooling system?

Its a bit high, I would recommend downloading MSI Afterburner and setting up some fan profiles.

You can set a curve to turn up the fan automatically. Like at 70C, the fan speed goes up to 75% or something like that:

http://event.msi.com/vga/afterburner/download.htm

You don't need an MSI card before you ask.

Not really unless you are willing to pay $50-90.

My GPU came with software called 'Thunder Master' which allows me to do the same thing. I can either set a static fan speed, or a automatic one which adjusts dependant on the temperature.

I can't seem to find what it is, but if it works the same then set it to automatic. I just like Afterburner because you can set a curve, so the automatic isnt making the card blow and make noise all the time.

So is 80C too high for a load do you reckon?

Its nothing to worry about, but its still a bit high.

If it hits 100C then I would worry, not at 80.

Any tips on how to cool it down?

Here's where I stand the PC:
http://img411.imageshack.us/img411/3576/dsc0006cd.jpg

This is with the side fan:
http://img266.imageshack.us/img266/1530/dsc0008jy.jpg

This is without the side fan:
http://img411.imageshack.us/img411/6299/dsc0010xj.jpg

80 is an O.K. temp for GPU heavy games. But for Minecraft? You have a cooling problem.

I just ran Minecraft with it on my other screen. It sloooooooooooowly crawled up to 68-70 and stopped there.

I will be testing it with CoD/Crysis 2 soon, they're downloading.