Best NA deal was traded a Casino Kid II cart that I got Complete and kept the IB from trading in free DVDs to the local gamestore for CIB mega man 64, CIB American Tail, and couple other boxed games back when they were still $20-$30 games.
Best in the wild deal would have been an Gottlieb Incredible Hulk pinball machine I picked up for $25 that was said to be non-working. Got it home and plugged it in and it worked perfectly sold it next day for $1k.
Best Ebay deal was a complete boxed set of the 7 North American released N64 controllers Extreme Green, Grey, Black, Blue, Yellow, Red, Green for $120.
Sadly I sold all of those when I quit collecting and now going to have to pay a premium to get them back.