Lower Ball joints and replace your radiator.
Do the lower ball joints and radiator first. If a ball joint fails your best case scenario is a very expensive repair bill that could have been prevented with $160. Only use oem lbj's. Google 4runner lower ball joint failure. Basically your wheel falls off while you're moving.
If your radiator (really the transmission oil cooler) fails, you've got to replace or rebuild your transmission. Also very expensive.
If your timing belt breaks, your engine turns off but it doesn't cause any collateral damage. You just replace it like normal. You don't have an interference engine. It needs to be done, but I'd give higher priority to those other two.
I'll go ahead echo what everyone else has said about the Lower Ball Joints and radiator. Lower Ball Joints need to be at the very top of your list. Everything else can wait until that's done. Don't fall into the mindset that it's too expensive or that yours seem to be working ok.
And above all else, they need to be genuine Toyota Lower Ball Joints. Part store brands are NOT acceptable in this instance. If you are not going to replace them yourself but have a shop do it, be damn sure to bring them the OEM parts. Don't let them slap on some cheap junk from Autozone. OEM only.
This is what happens when one of your LBJs fail:
http://www.toyota-4runner.org/3rd-gen-t4rs/227083-one-more-lbj-failure-add-list.html
Ok so the quote I got from the dealership for:
radiator - $563
LBJs - $633
timing belt/water pump/engine seals - $868
alignment - $89
Grand total out the door - $2328.06
Seems pretty high but of course it is a dealership..
What do you guys think?