There's a train station near the airport (also for the National Exhibition Centre) and this is the quickest way into Birmingham. Trains don't run at night though, so if you're travelling late at night you may need to take a bus.
Train
The airport is well connected to over 100 towns and cities in Birmingham by various operators: Virgin Trains, West Midlands Railway/London Northwestern Railway, Cross Country and Transport For Wales. Here are some of the destinations by train provider:
Virgin Train: London Euston, Birmingham New Street, Wolverhampton
West Midlands Railway/London Northwestern Railway: London Euston, Northampton, Milton Keynes, Birmingham New Street, Rugby
Cross Country: Manchester Piccadilly, Bournemouth, Birmingham New Street, London Euston, Northampton, Coventry
Transport For Wales: Shrewsbury, Aberystwyth, Holyheasd
To take these trains, you must first reach Birmingham International Station by taking the free monorail Air-Rail Link service. These trains run continuously and the journey takes less than two minutes.
Cost: From GBP 2.40 one-way (depending on the time of day, or if you buy your ticket online)
Location: Take the airport monorail at stop D to Birmingham International Station
Taxi
Hackney carriages (black cabs) operate from the airport 24 hours a day. Taxis are metered, but you can secure a better price by pre-booking your taxi, either online or at the airport. Journey time into the city centre is around 20-30 minutes.
Cost: Around GBP 30
Location: Taxi rank opposite the main airport entrance
Bus
There are currently three National Express buses which connect the Airport and/or Birmingham International Station.
Bus services:
X1 (connecting Birmingham City Centre and Coventry) - Bus stops K & J on-site
X12 (connecting Birmingham City Centre and Solihull) - Bus stops K & L on-site
75/75A (connecting Sutton Coldfield and Birmingham International Station) - Bus stops NB & SB at Birmingham International
Cost: GBP 4.10 to Birmingham or Coventry, from GBP 4.00 for a day ticket
Tip: To save money, you can also travel on discount bus company, Megabus. Tickets can only be purchased online, for as little as GBP 1: www.megabus.co.uk