Good for general London information – restaurants, things to do, places to try:
Time Out
The Londonist
Hype! App
Time out and The Londonist have good mailing lists to sign up for and receive daily/weekly email updates about London events.

Good for planning nights out:
Resident Advisor
YPlan App
Designmynight
Latenight
The Londonist Best Pubs

Good for transport:
Barclays Bikes
Citymapper
TFL journey planner
Hailo
Uber
Addison Lee