A few events that may have slipped beneath your radar:
If you missed out in the ticket scrum for Esa-Pekka Salonen's Philharmonia Tristan und Isolde at the Royal Festival Hall with Gary Lehman and Violeta Urmana, you might consider travelling to Birmingham Symphony Hall (where the sound is also immeasurably better) on 23 September 2010 for the UK premiere. Not many tickets left so don't hang around too long.
Birmingham is also the furthest south that Opera North will bring their new Das Rheingold (semi-staged) next summer. It's on 24 June 2011 and there are plenty of tickets left at the time of writing, though the best are going fast.
Antonio Pappano and the Royal Opera House orchestra take a rare step outside Covent Garden on 27 February 2011 when they perform at Cadogan Hall. Thomas Hampson and ~Klaus Florian Vogt~ join them for the chamber version of Das Lied von der Erde, with Wagner's Siegfried Idyll also on the bill. Tickets went on sale yesterday.