Hi Andy,
Welcome to our world

. There are scales out there other than 1:16, but I have no experience of them so I will leave it to the others to comment on their merits.
1:16 tanks come in 2 forms - Kit and ready to run (RTR). the RTR brands are WSN (a RTR off-shoot of Trumpeter), Heng Long (and the related Matorro brand), and Hobby Engine.
By far the most commonly available is Heng Long (HL). The have been around for a few years now and their quality is much improved from when they started out. Not including the variations in paint schemes, different levels of electronics - so called 'Smoke and Sound' (S&S) and non S&S - and the choice of Infrared or airsoft armament, HL offer 11 different models.
There is also a wide range of available upgrade and detailing parts, modification kits, and most importantly - easy access to spare parts when something breaks! The newer models come with Infrared battle capability as an option, with upgrade kits being offered for the older models. This is not compatable with the standard used by the majority of RC clubs around the world, but its plenty good enough for you and your son to chase each other around the back yard
Matorro are a 'somehow related' company, formed by 2 of HL's distributors (Mato in Canada, Torro in Germany). They currently offer 3 models, but they are more expensive and a little harder to come by in the UK. As a general rule, because they are more of a niche brand their quality/robustness isn't quite upto HL standards yet - most of us here tend to either replace the gearboxes and/or the electronics.
They do have a Sherman in the works right now, on which they have been working with one of the more respected modellers in the RC community on the design, we have high hopes that they will take a giant leap forward with this release.
WSN market modified versions of the Trumpeter T34 and Tiger static kits. The electronics are poor and most of us replace them immediately with the cheap and readily available HL stuff. The tanks themseleves are also not quite as robust mechanically, and the spare parts are harder to come by. That said, they do come with a much better paint job that the HL tanks. The newer versions also offer "infrared battle" capability, but again this is not compatable with any other brand (and the fact that you can hit the other guy whilst virtually facing in the opposite direction makes us wonder why they bothered...!)
The Trumpeter static kits are generally more hassle that they are worth to make into an RC model. They are working on an RC version of their M16 half track kit however, hopefully for release later in the year.
Hobby Engine have 2 models at the moment, the M1 Abrams and Leopard 2. As far as I recall from reports, once you have replaced the electronics they are ok - check with Mackem if you are interested, he's our resident Hobby Engine guru.
Your choice of Kits are as follows:
Tamiya I'm sure you are familiar with. Their latest 'full option' kits are the best models out there currently, and by far the most expensive - going by US prices they are 6 to 8x the cost of the equivalent HL tank, if you factor in the price of the additional radio gear you need to buy on top of the kit. Beware of older Tamiya tanks available second hand - only the latest 'full option' models have turret rotation, sounds etc. The older models generally need a lot more work and extra parts (usually HL again) to bring them up to the same functionality as a RTR HL tank. They currently offer 6 WW2 and 1 modern tank, with another WW2 design in the works.
Andrew Design are a niche market manufacturer, they make some very nice resin kits of some of the less well known German WW2 armoured cars and support vehicles. They are also suitably expensive for what they are, and might not be the best thing for your son to be playing with right now...

See
www.xion.de for their range.
Hooben are a new company who are looking to get into the market. They are looking to be the Chinese equivalent of Tamiya, offering a quality kit with 'full option' type functionality. At the moment they are ironing out the electronics of their T55, with other tanks slated for release later in the year. the cost should be roughly half way between a low end Tamiya and a HL.
So, at the end of yet another rambling essay from the Ex_Pat:

Generally I would recommend the Heng Long smoke and sound range as a good source of starter tanks. Assuming that you don't get landed with somebody's old stock (beware of the cheaper examples on Ebay!) most of the original bugs have been ironed out of the Tiger and its not a bad start point to build on over the coming years. Avoid the 'Panther'

,the rest of their line up is ok so long as you bear in mind that they are a toy and if the thing starts struggling to move, its probably best that you stop before you blow a transistor or something...! (Even the Tamiya's aren't bullet proof in that regard - despite what some might tell you elsewhere...)
The WSN's are certainly attractive models, and different to what HL offer (Mid production model Tiger vs Early from HL). If you feel up to the challenge of gutting them and replacing the electronics then go for it, otherwise they're probably best avoided due to the lack of available spare control boards. The rest I would hesitate to recommend for younger children due to a lack of robustness and/or high cost, but at least I hope you have an idea of what is out there.
If you wish to get involved with our club, your options for suitable electronics and IR systems can be found here:
http://www.rctankwarfare.com/Forums/ind ... 919.0.html
Recommended vendors can be found in this board:
http://www.rctankwarfare.com/Forums/ind ... ,17.0.html
I should warn you that these things are addicitive and you
will own more than one...
Hope this nonsense helps!
Mart