I saw DC United vs LA Galaxy last year i think, all the big guns in the galaxy squad including Beckham. They got battered 4 - 1 and the standard was very poor. The stadium and the atmosphere was very good though.
About 6 years ago I caught a pre-season between Barcelona and Boca Juniors at the Nou Camp and it Ronaldinho's debut with Tevez and Mascherano turning out for Boca.
In Milan for a stag do in April this year, went to A C V Catania - a great game that finished 2 - 2 with A C coming back from 0 - 2 down.
I've never been in a more crazy atmosphere in my life. Flares, flair, weed, explosives, fighting, racism, and not one single steward. Oh and it only cost €16!
Seen a few games while on holiday in Cyprus. The best was Anorthosis v Inter Milan in the Champions League the season before last. The Cypriot team came back from 1-3 to draw 3-3. Great atmosphere with flares and flags and noise.
Siena v Milan (Serie A)
Portugal v Denmark (World Cup Qualifier)
Porto v Fenerbahçe (Champions League)
Atlético Madrid v Sevilla (La Liga)
Sevilla v Atromitos (UEFA Cup)
Can Middlesbrough v Brighton & Hove Albion and Hartlepool United v Brighton & Hove Albion count? We didn't come home between the two games, so it must have been a holiday.
SC Freiburg in Germany against Eintracht Braunschweig
Sparta and Slavia Prague once each, and the mighty Viktoria Zizkov four times. All in the Czech Republic.
I sort of saw Leverkusen vs Muenchen 1860 play once. I had food poisoning, so I spent most of my time in the toilets. I remember hearing English voices from the cubicle.