Not much, nothing major or expensive.
The battery died and was replaced in about 2007.
I think the timing belt was replaced around 70k miles.
The starter had to be replaced in 2008, and the body started to rust before we bought it, so we couldn't prevent it. It was only surface rust, so in 2008 the lower 1/4 of the body of the car was painted with truck bed liner...
I absolutely hate my Geo, but it has been extremely reliable. My parents bought it in 2004 for my step-mom's winter car (she drives a BMW during the summer), it had 63k miles and they paid $3000. Now going on almost 6 years and 45k miles, it's required MAYBE $1000 of repairs or maintenance (including oil changes and basic stuff like that).
It's really slow, it's definitely not a highway car, I have to put it to the floor to pass vehicles or just got 65mph up a hill. I feel bad doing this because the tachometer goes to 6k RPM's and the wind easily blows you around.
Mine gets horrible MPG's, I'm getting around 18MPG if I'm lucky, the winter is even worse.
I have a love hate relationship with this car, this winter was the straw that broke the camels back though. We had some -25*F weather, the first day it started fine, the next day it was dead so I had to start plugging it in over night.
The doors would freeze, I could get in, but then the door wouldn't shut.
The shifter sometimes won't move out of park.
It puffs white smoke when I first start it, and sometimes the remote starter doesn't start the car.
The 4WD system is annoying; luckily I have the automatic wheel hub things, so I don't have to get out to put it in 4WD, but having to stop to put it in sucks because I lose momentum so I get stuck. Then having to back up after taking it out is annoying, because I have to make sure no car is coming, so I just quickly back up and be on my way.
But, even though I have given more cons than pros about this car, it really has been a good car. It won't die! (sometimes I wish it would, but it won't)