Electronic Plastic is an online museum with pictures and info of more than 900 handheld electronic games of the retro kind, as collected by Jaro Gielens, who has been collecting them since 1981. Every entry is from his personal library and he kept the original package for all of them. It has all the famous models from Tomy, Tiger, Nintendo and other top companies, but countless obscurities too, searchable by name, technology, and even case color. The latest entry is Space King, made in 1983 and "one of the rarest VFD [vacuum fluorescent display] games."
There a book to go with the collection, but it's out of print. Here's an interview with Gielens.
I remember being fascinated by Mattel's Dungeons & Dragons and hankering for Tomy's Space Turbo; the last one I remember actually owning was Tiger's Street Fighter 2, not in Gielens' collection and, if we're being honest with ourselves, objectively the worst post of the game. Nowadays you can buy the real game in the same form factor for $40 at the same shop your grandmother buys her underwear.
Previously: Sega's OutRun hacked into a Tomy toy dashboard