Let's see here... The best deal I could've had, but was too young to know any better at the time (even though I had the money in my pocket for it) was a gray NWC for $5 at the flea market in Dalton, GA, back in the summer of '91 or '92. Some deals I've found over the years:
1. Sega Master System, 22 games (all but one in original cases, 13 of them had manuals), 3D glasses, hookups, 2-3 controllers (I forget how many controllers for sure)... One of the 22 games just so happened to be James "Buster" Douglas Knockout Boxing, with original case. That bundle, plus two 3DOs (systems only...I figured eh, what the heck?) and 17 fairly common NES games (I think the rarest of the bunch was Silent Assault). My cost? $55 for the whole lot. Buster Douglas came out of that bundle, and went into a deal for...
2. ...Flintstones: Surprise at Dinosaur Peak, NES (cart only, not-so-good label), plus one other game, for Buster Douglas Boxing and Mega Man X3 SNES.
3. 24 boxed or complete primarily common to scarce NES games, as part of a large lot, for $40. As it turns out, those weren't the only boxed NES games I ran across that day...I had bought another 10, plus 4 loose carts, from another guy for $35 (one of them was Magician CIB w/everything).
4. Sega Master System CIB, Light Phaser, Hang On/Safari Hunt pack-in, for $20.
5. SNES w/7 loose carts, including Super Mario All-Stars and Secret of Mana, for $20.
6. Final Fantasy, NES, factory-sealed (yes, legit), for $18.xx shipped off eBay (it was a few years back, 2004, if I recall correctly). Ended up selling it

.
7. Final Fantasy III, SNES, loose, for $1.50 (at GameStop...lol).
8. Panzer Dragoon Saga, Saturn, complete and super-mint, for $110 shipped. Some months later, picked up a complete Shining Force III from the same guy for $40 shipped (slimshadow at TGN).
9. A trade, his Levinson electric guitar (last one that sold at eBay went for $1750 Australian + shipping) for my complete Grandia (PS1).
10. A large lot of super-mint PS1 strategy guides (35 total), not the least of which were guides for Alundra, Alundra 2, Breath of Fire IV, Chrono Cross, Dragon Warrior VII, Final Fantasy VII, Final Fantasy Tactics (original version), Legend of Dragoon, Legend of Mana, Suikoden II, Tactics Ogre, Tales of Destiny II, Vandal Hearts II, and Xenogears, for $175.
11. A boxed Atari 2600 (lite-sixer), w/9 games, hookups, 2 joystick controllers, and 1 set of paddles, for $5.
12. A brand-new top-loader NES for $50 (back when they were retailing for that...does that count?),
Those are what immediately comes to mind.