Depending on region the recommendations will change. I am in US so historically the 2 biggest brands (meaning most used options and easiest to find info on) were Innova and Discraft.
The App U-Disc will show you most courses in your area regardless of location.
The Buzzz is the most popular disc in the entire sport by sales numbers and is a midrange. If you play with only one disc, the midrange is the best disc to use: It is easier to learn for beginners, but can still let you do a variety of throws once you are more experienced.
Other good and larger brands are the trilogy brands (Westside Discs, Latitude 64, and Dynamic Discs) They are three brands that are all owned by the same company, and have very similar plastic with different names. Dynamic is based in Kansas while the other two are Scandinavian. This just means that it will be easier to find Dynamic discs in a generic sporting goods store, but all 3 are well represented online and in specialty stores. These three brands discs also float in the air a little more easily which is good for beginners and those with weaker arm strength.
I’d recommend finding a used midrange (and ignoring all the crazy numbers at first) and seeing if you have any interest in the sport. If it’s around 10-12 dollars or less, it will be the brand’s entry level plastic. These typically feel harder and grainy. They work great, but hitting trees can dent or chip them which alters the flight. Great for starting out, but not what you want to use all the time if you start playing more. Above that price and you will start getting into other plastic blends which are typically more glossy, rubbery, or see through looking and have their own sets of pros and cons. All of them are significantly more durable than the entry level plastics though. The entry level plastics for the brands I have mentioned are:
Innova - DX
Discraft - X
Dynamic - Prime or Classic
Latitude 64 - Retro or Zero
Westside - Origio or BT
Some Midrange Recommendations by brand mentioned:
Innova: Roc, Roc 3, or Mako 3
Dynamic: Truth or Justice
Westside: Tursas or Bard
Latitude 64: Claymore, Fuse or Compass
From there, there are a lot of resources online, or I am happy to share what I have learned through the years (I’m no professional, though my roommate of 3 years in college won a national championship in it).
If people enjoy and are interested, I’ll set up a topic for it so I don’t flood this one with info.