Has it been overheated (was that why the water pump was replaced)? - If yes then you'll have to worry about warped heads, I don't think there's a good test for that besides sniffing the exhaust and checking the oil for coolant.
How many miles are on it? - More miles the more maintenance it will need
What does the trans fluid look like? - Black = bad, if there's metal flakes or pieces it probably needs a new trans and I'd stay away
Has the timing belt been done? - Not super important because it's a non interference engine but it's good to know
Is the oil 10k miles old? -These engines are much happier with 3k oil changes
Take it for a test drive and feel for the transmission slipping or slamming shifts (slipping it will rev up and not go anywhere, slamming into gear you'll feel it buck on the shifts), you'll want to get it warm to do this test. Also see if the check engine light is on and check the codes, that will help reveal any hidden issues.
Checking for oil leaks is a good idea as well. Check down around the bottom of the engine to look for leaks on the main seals and oil pan, then check around the valve covers and pull the spark plug boots and look for oil down in the wells. If you find a lot of oil down in the wells new valve cover gaskets are going to be needed at some point.
Most importantly though, CHECK THE HEATER. Get the car warm, crank up the heat and rev the nuts off it (to get the water pump going at full pressure), if it smells like coolant or the window fogs up, don't buy the car unless you have a weekend to spare or don't want heat. The heater cores in these cars like to fail and it's a massive pain the @$$ to replace it (you have to take out the dash board). Stop leak will work for a bit but then it will explode at the Fred Meyer gas station and make the attendant lady very cross.
I'm sure I've left some things out but those are what I'd look for.
