The coolest thing I've found, by far, was a Dell Inspiron E1505 laptop computer. I didn't find this in the trash, but on the side of a road near the end of summer when the rich college kids moved out. It didn't have a power adapter, and I was only able to get it to turn on once with a spare power adapter I had, but it only turned on once. So I just put it away in my closet. Then oddly enough, a few months later I came across a Dell power adapter that exactly matched this laptop in the trash near campus. I plugged it in, and it booted right up. So I got a brand new (to me) laptop. Kickass.
I found a pair of Beats headphones in the trash near campus. The top foam headband was missing, but a bit of spare fabric and I was able to make it look mostly normal. I assume the owner threw it away since the top headband came off, but other than that, they worked just fine. Now, these headphones are not worth the $200 dollars they seem to cost, but they sound decent enough, especially for something I found for free.
I've also found a number of Apple ear buds, and also ScullCandy ear buds. Although most of these have broken cord connectors, where one channel doesn't work, but that's easy enough to fix with a spare jack and some solder. Just yesterday I found a completely working pair of House of Marley Midnight Ravers ear buds, and they sound pretty decent. They also have a nice fabric cord, which doesn't tangle as easily and is more durable. Ear buds are not my favorite type of headphones, since they just don't stay in my ears, but it's always nice to have a few spare sets lying around, in case I need them.
I've found a number of random cords, like audio/video cords. I found 2 HDMI cables just a few weeks ago, and those are always handy. I've also found a bunch of network cables. I found a 100 foot cat6 network cable, which was a nice find.
Along with the bottles of unopened beer I've found, I've also found bags of candy and backed goods, such as donuts. Yeah, you may think that eating food out of a trash cans is gross, but this is food that hasn't been opened yet, so I figure it's still good. I found a 9 pack of Cinnabons, that were still sealed, and that was a delicious bit of food I found.
I've found a number of cigarette packs, with all but one still in the pack. I'm guessing these are cigarettes that people who "quit" bought, just to have one smoke to hold them over. But they threw the rest out, and that's a nice find for me since I also smoke.
During the time that the rich college kids moved out, I found a dorm refrigerator. It was a pain in the ass to get home on my bike, but it was a nice find, since my sister needed one since her refrigerator broke around that time.
I've also found just strait up cash on the ground. In total, I've found around $50 bucks on the ground. Usually outside of bars (I'm guessing the cash just fell out of their wallet as they put it in), but I've also found bills just lying on the sidewalk. I find coins a lot, but the bills are the best.
I found a keyboard in the trash. It was a bit dirty and the labels were worn off on some of the keys, but it worked fine other than that. I gave that to my mother since the one she was using wasn't shaped to her liking.
I've found various backpacks just chucked in the trash. Most of the time these are empty, but sometimes they have loose change in them, and once I found an LED flashlight (that I now use to look in trash cans).
I've found a number of coffee mugs and water bottles. I take these home and wash them out, since it's always handy to have coffee mugs around. Oddly, in one coffee mug (some Starbucks coffee mug), it was full of water, with what looked like flower buds inside. I don't know if that was some fucked up hippy drug, or if it was some herbology student project. But I didn't investigate very hard. I just threw it down the disposal and washed it out.
On two occasions, I've found dirty porno mags in the trash. This sort of amuses me, since I thought people used the internet for porno needs nowadays. I took a looksy through them, and thew them back in the trash, since the internet is for porn.
I found a coffee maker on the side of the road, but maddeningly, the owner cut off the power cord. But I took it home anyway and repaired the cord, and it seems to work just fine now. Always good to have a spare coffee maker, in case the one I have now breaks.
I'm sure there's other cool things I've found, but that's all I can think of for now.