100%+ The best returns on your tech gear is going to be your vintage equipment, like the enviable example shown above. Of course, these are quite rare but if you, your parents, or grandparents have anything in their home that they've had around for decades, you might be in luck. Particularly rare/highly coveted tech are the designs of legendary designer Dieter Rams. His products will always fetch a higher price than what they sold for originally due to their importance to the history of industrial design, like this extraordinary Braun SK55 record player (nicknamed Snow White's Coffin) which now sells for upward of $2727 via specialty retailers and occasionally on eBay. Records are another good example of tech which has the potential to greatly exceed its initial retail value due to limited releases or out of press status. iPhones also have the potential to sell for way more than their retail price if you purchased with the subsidized rate and later sell for more.
50%-75% As long as the tech is between 1-3 years old and is in good condition, you can expect electronics originally priced in the $300+ range to fetch anywhere between half and 75% of its resale value. This includes things like laptops, popular phones, tablets, etc. Generally, as long as the product is decently performing, you can expect it to get a fair price. Typically, people who purchase things like laptops second hand aren't in need of the latest and greatest so the specs are a bit less of a concern as long as it can still perform the standard functions well.
30%-50% This category is when things start to get a bit rough. In our searches we found that things like printers and scanners generally sell for less than half of their retail value. Probably because their newer versions aren't very expensive and easy to buy new. DVDs also seem to fall somewhere in this area as well.
10%-30% Lastly, the bottom of the barrel is the outmoded tech. The used CD market has dried up considerably due to digital downloads and the rising interest in vinyl. Trying to resell CD collections can be very difficult unless you're willing to settle for $.25-$.50 for each album on average at used CD shops. Radios are another example. Perhaps finding creative reuses for some of these products might be a more valuable outcome than selling them for profit. (Images: Trendynet, Flickr Creative Commons: Incase, Mary-Lynn, Silvia Viñuales licensed for use under Creative Commons.)