Are there any good marketplaces to sell a high quality site which generates over $5,000 a month in revenue?
Flippa seems to be the only one I've come across, but most of the sites listed on there appear to be spammy. I am not convinced buyers with deep pockets would browse Flippa to buy sites.
What are some other such places to sell a website?
Usually for smaller sites, making in the region of $500 per month, we'd recommend marketplaces such as Flippa (which you've looked at) and also FreeMarket
If your website is making between $5k-$1m net per year you might be better of speaking to an experienced website broker. They can help you maximize the value of your website before a sale, remove time wasters because they have a pre-qualified list of buyers and do the heavy lifting for you.
FE International can give you a free confidential valuation. Speak to Thomas.