A Gold Card is an annual season ticket for journeys starting, finishing or wholly within the Gold Card area, and issued within the Gold Card area. From 2 January 2015 this area expands beyond the London and South East to also include all Abellio Greater Anglia services except Ely - Peterborough, East Midlands Trains from Norwich to Ely, all Chiltern Railways services including to Kidderminster, London Midland to Stafford, the West Midlands, Shrewsbury and Worcester, and Arriva Trains Wales from Birmingham to Shrewsbury. Virgin Trains and East Coast services, and Cross Country north of Banbury, are excluded.
A Gold Card gives you and up to 3 adults travelling with you 34% discount on off-peak tickets (ie after 0930 Monday - Friday and all day Saturday and Sunday), with no minimum fare, for any journey wholly within the Gold Card area - not just the journey covered by the season ticket. It also gives 60% off child tickets with a minimum fare of £1. Discounts are also available on London Underground.
The cheapest season available as a Gold Card will be Lichfield Trent Valley to Lichfield City at £144 for the year. You don't have to go to Lichfield - you can buy the annual season at any station within the Gold Card area - just make sure that it is printed on gold card stock. The Ryde Esplanade to Ryde St Johns Road season costs £168, but if bought at a South West Trains station it does also include six free tickets on South West Trains each year.
If you are under 25 or over 60, then this probably isn't for you - the 16-25 Railcard or Senior Railcard give similar benefits for just £30 per year. If your travel is within the London and South East Network Area and is only at weekends or your individual tickets cost over £13, then you may find that a Network Railcard is a better deal at £30 - it offers 34% discount on off-peak tickets but with a minimum fare of £13 on Mondays to Fridays.
Disappointingly, London Midland have anticipated a rush for the Lichfield City to Lichfield Trent Valley annual season by hiking the price to £144 for 2015, a rise of 33%. However you can avoid this increase by buying the ticket before the end of 2014, for only £108. You just have to return to the station ticket office where you bought it to get the ticket reprinted on gold card stock (at no charge) at the beginning of 2015.
Full Gold Card benefits and terms and conditions
Gold Card area map
Rail User Help gives more ways to save money on travelling by train.