Friendz is more hard trance / hard dance but is an excellent party [shameless plug] and I'll be back playing there next month [/shameless plug]
For trance I'd recommend...
Knowwhere - uplifting trance - currently at The Soundshaft but moving to the Fridge in May
Tilt - trance / hard trance over two rooms - at Studio 33, Vauxhall (next one is this saturday 3rd April)
Edition - uplifting trance once a month at Freedom Bar, Soho
Spangulation @ Club 414
'Ground Zero Productions' - watch for "one off" promotions run every 3 or 4 months. Each at a different venue and tailored to make each very different (e.g. A villa party in Ibiza, thames river boat party, 'cocktail' party at a very cool central london bar)
They'd be your best bets for quality music run by good crews