Far too many to mention, but thinking about it, if I could go back in time I'd go into the foreign office circa-2003 and deny a certain Mr Abramovic a visa to enter the UK. Or at the very least, divert his helicopter away from Stamford Bridge after flying away from having his offer to buy Spurs rejected. Then Chelsea would have crumbled under debt and become the next Leeds United.
Why would that have made such a difference to us? We have finished 5th, behind Chelsea, in five seasons since, and also lost a Champions League spot to them in 2012. Now even putting aside the fact that they've gazumped us by at the last minute with ridiculous wage offers for players like Mata, Oscar, Hazard, Willian etc over the past few years, there's very good reason to believe that, had Chelsea crumbled in 2003 like they deserved to after years of Captain Birdseye overspending, we'd have established ourselves as Champions League regulars. Not having CL football meant we lost Carrick just as we signed Berbatov, we lost Berbatov just as we signed Modric, we lost Modric just as we signed Lloris, we lost Bale just as we signed Eriksen etc. I also think that, had Roman not done it first, we wouldn't have seen first Thaksin and then the Sheik pump money into Emirates Marketing Project. And after years of biding our time, waiting for one of the established "big four" to drop out, when Liverpool finally did fall to pieces then it was City who wrestled in ahead of us to take their place.
We've had some fantastic players over the past decade, imagine if we'd been able to keep them together and add to them with the quality that CL football and money could bring.
Or if we're going for an on the pitch moment - somebody should have taken out Henry just before he equalised in the last NLD at Highbury. Not only would we have ceremoniously ended their old stadium, as well as the Arsenal careers of Campbell, Pires and Ljungberg, but it would have made the lasagne-gate irrelevant as we qualified for CL ahead of them. Regardless of what they may say now, they had absolutely not considered the possibility of failure to qualify for CL that year and given the debts they were in and the years of austerity that were to follow, they would have had to sell Henry in order to stay afloat. We'd have got to see Carrick and Berbatov playing together in the Champions League for us too...