I have old items that I want to sell for bitcoins. This includes digital content and physical objects.
What websites can I use to sell them?
You can find an extensive list on page Trade at Bitcoin Wiki.
A short list of some auction sites that use Bitcoins:
If you want to sell digital files per download, go here: http://bitcoinservice.co.uk/ .
And as with anything, you can just post on an online classified ad websites, such as craigslist (thanks Thilo for the suggestion).
For digital content, coinDL is worth a shot: https://www.coindl.com (full disclosure: it is developed and operated by myself).
You can also post your goods & services on BitcoinTrading.com: bitcoin buy/sell classifieds.
http://CheaperInbitcoins.com You can buy or sell as many items as you want for free, you only pay for upgrades. You can sell items anonymously and as the owner I can vouch for my self and say that we are incorporating our website with an up and coming Web Of Trust ratings system to provide safe, secure and anonymous person to person transactions.
If you are selling a digital product you can use http://instabuck.com/
I've never used it for this purpose but I believe Mokimarket allows you to sell items in a penny auction format.