It can be a daunting task finding a suitable recorder, whether for beginners or for more advanced players. I think one of the most exciting aspects of my instrument is the sheer variety of sizes and shapes and sounds to explore.
But to start with, you need to get a reliable instrument which is in tune, has all the notes, and makes a decent sound.
I will concentrate on beginners' instruments for children to keep it simple for now! Children will usually start on the descant/ soprano size recorder so fingers can cover the holes easily. For plastic recorders, I would recommend either Yamaha YRS302B or the YRS312B descant/ soprano, or Aulos 205 soprano/ descant models. These are between £10 and £20 usually but you can shop around on the internet. It is important to get the right model numbers however - other models by the same makers can be radically 'different', to put it politely!
For a slightly better sound and a hint at what is to come when you enter the world of wooden recorders, there is a recorder with a wooden lower piece and headjoint made from plastic. This is a clever option, as the delicate top joint can easily get damaged when made of wood, and to start with, it can be safer to opt for the tougher models. The best of these in my view is made by Mollenhauer, the Prima soprano (there are a few model numbers here - all good - 1095, 1074, 1064, 1094 etc). They are about £28 at the moment. A word of warning, try to steer clear of cheap wooden recorders if they are not recommended by an expert teacher - they are often worse than plastic recorders.
Do have a look at the Recorder Centre website (also called the Early Music Shop), or go to the shop on Denmark Street. They are very helpful, and it is particularly useful to try their selection first when you are looking for a good wooden recorder. See www.earlymusicshop.com for details.