First of all, welcome back to RailUK Forums!
Looking at your location and user name, I guess the London area would be a good place to start.
Southern have introduced 26 Class 377/7 trains- 5 cars in length- for metro routes (although they have ended up on Brighton services occasionally). All 26 units are now in service and this has allowed them to withdraw all 24 Class 456'a (more on that later!
). Southern are now going to receive 8 Class 377/7's, also 5 car, but they are dual voltage and are to be used on the South Croydon to Milton Keynes route. I know a couple of units are being tested. I'm not sure if any are in service yet (I live in Nottinghamshire, so it's not an area i'm too familiar with
)
South West Trains have started to receive their Class 458/5's. Do you remember the Class 460's on the Gatwick Express services? They have taken them up to Wabtec at Doncaster and are essentially merging them with Class 458's. This will turn the 458's from 4 cars to 5 cars, but their top speed will be reduced to 75mph. This is where things get complicated: The 458/5's will then go the the inner suburban routes (e.g. Hounslow loop and Windsor and Eton Riverside), allowing the Class 450 HC's to have first class re installed so they can be moved back onto outer suburban routes. The 458/5's will normally operate in a 10 car formation (2 units)- all this is about getting a 10 car railway for London suburban services (part of the High Level Output Specification I believe). The Class 456's from Southern have been transferred to SWT. They will be refurbished in due course (in Southern livery/Southern interiors currently) and will allow some 455 operated services to become 10 cars. The are also now operating the Guildford to Ascot services instead of the Class 450's.
Elsewhere, First Transpennine Express have received 10 Class 350/4's- basically the usual Class 350's but with an intercity layout- they have 3 toilets instead of the usual 2. They are being used on the Manchester Airport to Glasgow/Edinburgh route, releasing some Class 185's to allow FTPE to run a fifth train per hour between Manchester and Leeds from the timetable change this month. The service will run from Liverpool Lime Street to Newcastle via Manchester Victoria, and the current Manchester Airport to Newcastle service will be cut back to York. All units are now built and delivered.
London Midland will soon take delivery of 10 new Class 350/3's. I think it's just to increase their capacity. I don't know much about this tbh. I've seen a video of the first unit in testing. It was the London Midland order that FTPE tagged onto to get their units.
Finally, the Class 121 used by Arriva Trains Wales on the Cardiff Queen Street to Cardiff Bay shuttle has been withdrawn due to failures (can't remember what exactly). It is now being used as a source of spares. Chiltern's 121 is still going strong as far as I know.
Well, that's enough from me and is all I can think of from the top of my head. I'll let other members carry on.
Hope that helps.
Ryan