Until closing in 2013, Aristo-Craft made locomotives and rolling stock in 1:29 and 1:24 scales, as well as code 332 track, buildings, people, and a radio control system called the Train Engineer Revolution. The Revolution system is still available from Crest Electronics.
LGB practically started the hobby with 45mm track and a wide range of products. Many LGB products are based on European prototypes, with 1:22.5 (meter gauge) being the dominate (but approximate) scale. There is a wide-range of US products as well, not strictly adhering to any particular scale but sized to fit in with other G-gauge trains.
MTH makes a wide range of affordable 1:32 scale locomotives and cars, including big steam and diesel locomotives. MTH locomotives run best on DCS, a proprietary control system, but will also work on DC and, for 2014+ releases, DCC as well.
USA Trains is a manufacturer of highly realistic 1:29th scale and 1:24th scale model trains and code 332 brass track. USA Trains tends to keep a large inventory of items (including parts) in stock, and produces multiple road numbers for most equipment.
There are a lot of choices in large scale when it comes to power, sound, and control. Equipment almost always comes ready to run on DC power, but it’s often without sound. Many people choose to add to the experience with sound and independent control of locomotives using one of the products listed below:
As least locally AirWire (using battery power and Phoenix sound) seems to be the most popular control system choice, and for good reason since it’s easy to use and reliable. Although once you add sound and batteries it’s also one of the most expensive options. Note that QSI makes Gwire, which is mostly AirWire-compatible, so you have two manufacturers to chose from.
Locolinc has been around since the early 90’s. Today the system remains relatively unchanged, but the manufacturer still sells and supports the product. If you’re buying used equipment it’s not uncommon to find a Locolinc receiver already installed.
NCE makes a 10 amp DCC system with radio control which has proven to be one of the most popular DCC systems for large scale use. It’s not as cutting edge as some, but it’s reliable and affordably priced.
QSI makes sound and control systems which work with DCC, DC, or Airwire (using their Gwire receiver). Unique features include stereo sound outputs, and sound that varies with the actual load of the locomotive (uphill vs downhill).
Zimo is known for DCC sound decoders packed with features and functionality. They are also working on a premium DCC system which, when released, will likely be the most expensive but most popular DCC system on the market.