it's hard for me to throw anything out without first thinking about if it'd be a good bun toy.
Meadow has had laungry detergent pour cups (washed out very well!) she likes to pick it up and toss. sometimes roll it around.
egg cartons are popular too.
you can get baby keys (the plastic ones for pretty cheap)
dollar store untreated baskets or trash bins
boxes, boxes and more boxes
phone book, junk mail. i throw paper stuff in a box and Meadow ruffles thru it.
i have a four year old son and i have found that some kids meal toys are pretty good if they're solid plastic with no moving parts. Meadow will pick them up and toss or push around.
i'd definitely try getting some of the toys from here. they are really quite inexpensive and can provide a lot of entertainment. Meadow goes nuts for the willow stuff.
edited to add: if you are unsure about the safety of anything, make sure to supervise. Meadow has a few toys that are only supervision toys. they get taken away if i leave or go to bed.