I've been getting the same question a lot lately. I know I've talked about it here and there in the past, but everyone lately wants to know where/how I've been selling my stuff. I think it's my cash total breaking the $2k mark that's bringing on the interest. I've answered a couple times in comments, but thought I'd address it here where it will be easier to find. I have a few methods and it usually depends on what I'm selling.
Books, CDs, DVDs
I've mostly sold books, CDs and DVDs on Amazon. Know going in though, most used media items aren't selling for much and, as far as I'm concerned, not worth the time to list and ship. I always use delivery confirmation. Most buyers are very honest, but there are a few out there looking to get something for nothing so it's better for my peace of mind to cover my butt and not leave the option open for someone to say the item never arrived. I've donated many more of these items than I've sold, but have gotten lucky and been able to get some money back selling.
Yarn & Knitting/Crochet Books
I've had some luck selling yarn on craigslist. I usually put together a bin of mixed yarns and list it at one price for the lot, though I did offer some bag lots when I had multiple skeins of the same yarn/dye lot. I'm also a member on Ravely. If you like to play with yarn and you haven't gotten on Ravelry yet, do it now. It's free and an awesome way to find patterns and like-minded people. =) Anyhoo, there are lots of chat boards and a few are dedicated to destashing yarn, books and other fiber-related items. Most of my knitting/crochet books I've sold have been sold on Ravelry. I've also sold some yarn there as well. Again, I always use delivery confirmation to cover my butt.
Furniture and Miscellaneous
Other items, I've listed on craigslist. If the item is small enough to load into my Jeep, I arrange to meet the buyers in a public place. I have had a few larger items (furniture) that meeting elsewhere isn't possible so those have come to my home, but I really prefer meeting elsewhere just as a safety issue. You just never know who's going to show up. I routinely get frustrated trying to sell on craigslist though. There are a lot of flaky people out there so it sometimes take awhile to actually get a serious buyer. There are also a lot of spammers on there just looking to get your email address or phone number. When I list, I use the anonymous email option and ask that interested parties email their phone number and I call them. If the email is vague, 90% of the time, it's spam. If they haven't emailed their phone number, I don't reply. I'm sure I may have lost (or delayed) a few sales not responding to people who can't follow directions, but I'm okay with that. =)
So, I've sold quite a few items, but the majority of items have been donated. Small stuff isn't worth my time driving to meet up with someone. I have a limit. If I don't clear x amount, I don't bother selling. If I can't group items together and make a decent amount, it all goes into the donation box. Also, if I've been trying to sell an item too long, I'll often donate it. There are a few exceptions where with better timing, I know the item will sell. You just have to figure out your own limits.
There's my two cents. Good luck!
Dishwasher tablets. A friend who's really into couponing gave me these after getting a crap ton for free. These have been in my cabinet for nearly a year now. I was given these before I realized the dishwasher here leaks... and the idiot who put it in here actually punctured the tray in the bottom in two places using too-long screws. There were more pressing issues to take care of so the dishwasher has become a large dish drying rack instead and these are now heading to my neighbor who has a dishwasher that doesn't pee on her floor. =)