Hard to say really what deals I've had. I'm sure many people that bought a ton of games when they were younger like me to play from Gamestation, alot were anywhere between £1 and £5 so loads have gone up in value. Luckily for me I bought them to play so haven't looked much into what has jumped up the most as I can't remember all the prices!
I'd probably say the best deal I did was buy the Neo Geo CD about 16 years ago. I bought one, with most of the original box and 10 games for around £140 on eBay. The whole collection has gone across the board and are some of my most expensive games I own. I actually love the console. The controllers are fantastically made, like SNES but better. Super Sidekicks 2 is awesome and I've loved playing through it to win the World Cup. Lots of fighting games I have. I'll set it up next time people visit mine.