My best bargain is probably my sealed PAL Samba De Amigo (Game only) ~ I bought a package of about 19 sealed games for about £75. When the package arrived, I took the sealed Samba De Amigo, Deadly Skies, Tokyo Highway II, and Aerowings II out of the equasion, and resold each of the other games for a fiver each (They were sub-par common games, only worth a fiver if that, and I already had all of them apart from the four I took out), which meant I made my money back and got four games for free, of which Samba De Amigo was one of them! That game alone is worth the £75 I paid for the package!!! (I'm pretty sure the guy selling them didn't have a clue!)
Another good bargain is getting a sealed PAL Pokemon Stadium II for a tenner, after my local Toys R Us messed up and scanned the Pokemon Stadium II through as Pokemon Stadium I.
I also got my Limited Edition version of The Getaway for only £15, as the seller didn't have a clue how rare it was!!! As soon as I saw it go for auction at a starting price of a Pound, I eMailled the seller and asked if they would make it a Buy It Now for £15. I had previously researched normal versions of the game and they sold for around £8-£10 for a sealed copy, so I thought my offer was "Generous". Lol. And to my amazement the seller agreed!
Can't remember a lot of the deals i've gotten. I buy so many games, and don't really keep a record of how much I paid for things. I should really I guess.