Links

The point of the world wide web is for websites to link to other websites after all

General utility

random.org is an online random number generator with a lot of handy randomizing features.
PicResize.com is what I use when I don't feel like opening GIMP just to resize a picture.
WolframAlpha is pretty useful when you have an equation you don't want to work out. It can also deal with different units and even substitute the appropriate values for "Earth diameter" if you can't be bothered to look it up yourself.

Discogs about music releases and discographies
alldatasheet.com datasheets of semiconductor devices
elektrotanya manuals and schematics of old consumer electronics
hifiengine and vinylengine were great repositories of specs and manuals for hifi. However, the site regularly IP-blocks some regions, registeringg new accounts has been disabled for over a year now and existing ones are deleted without notice (who does that!?), all supposedly to stop some kind of abuse(?) from happening. If you can still get in, you should steal everything you can and then leave, that place deserves to burn and the friendly community of the vinylengine forum deserves better than this.

Tapeheads.Net a classic forum dedicated to magnetic tape recorders and any other hifi stuff
New XKCD forums a revival of the old XKCD forums, which was one of my favonline communities until it went offline following a breach (and yes, that is a dead link).

Eternal Jukebox makes any song go on indefinitely by finding places it can jump ahead or loop back seamlessly. Unfortunately the site on that link doesn't seem to work, but there are some mirrors here and here. If you use Ublock (and you should), you might need to turn it off for this.