This is how I cook bacon, and also produce almost perfectly flat bacon.
No special tools required (Well, I'm assuming most people have the following in their kitchen).
Tools Sheet Tray Cooling Rack (slightly smaller than the sheet tray) parchment paper (Optional, but makes for easier cleanup). BACON (I like the extra-thick cut).
Steps Take the sheet tray and line with parchment paper.
Lay bacon down on parchment paper.
You can fill the tray up, but I make sure the bacon stays in a single layer with no overlapping.
Place the cooling rack upside down onto the bacon.
This should keep it from curling.
Place into oven and turn oven to 400 F.
I don't find I need to pre-heat it, as, well, bacon isn't very complicated to cook.
In about 15 minutes or so, you'll have cooked, flat bacon.
(Adjust cooking time depending on your preference of crispiness.
Take out of oven and remove from tray.
(The tray and fat are hot, the bacon will keep cooking if you don't)
The cooling rack should keep it from curling while the fat slowly renders out.
As a bonus, I don't need to clean my stove after.
Alternatively, the mention of the George Forman grill reminds me of an idea I saw somewhere (might have been Good Eats), use a waffle Iron!
Use it just like the grill in Ward's answer.
cooking.stackexchange.com/users/231/talon8
This is specifically the reason for the invention of Bacon Presses
cooking.stackexchange.com/users/6563/Tremmors
A George Foreman -type grill does a good job keeping bacon flat, and also lets the fat drain away as it cooks:
cooking.stackexchange.com/users/266/Ward - Reinstate Monica
This is the way I cook bacon and
it almost always gives me flat bacon: Put the bacon in a cold pan.
Put the pan on the stove and turn it to medium heat.
Let the fat slowly render out and fry the bacon on its own.
Cook to your desired crispness
The gradual heating helps the bacon maintain its shape and is the best way to cook bacon, IMO.
cooking.stackexchange.com/users/9960/Daniel Chui
This is very old practical way to get flat bacon - take your cold water bottle from the fridge, pour into a dish or pan, and let the strips of bacon lay in the coolness.
In just a few minutes, the cool water will work its magic.
Then cook.
It will come out flat every single time.
This is an old trick from my great grandmother.
Don't dirty up a bunch of pans, or buy weights.
Just use cold, cold water!
cooking.stackexchange.com/users/18097/Roy Rolison
If you only need a small amount of bacon, microwaved bacon tends to be very, very flat.
Of course, it doesn't scale well to quantities for more than one or two people, in which case the oven method already mentioned is extremely effective.
cooking.stackexchange.com/users/14401/SAJ14SAJ
I've found that baking the bacon on a cooling rack (so the fat drips away) also results in flatter bacon.
cooking.stackexchange.com/users/6317/Yamikuronue
I made my own bacon press hack and it worked absolutely perfectly.
First you need really decent bacon as there are some brands that have killer qualities, but most brands are lackluster, especially supermarket brands.
One of these brands is Farmers applewood smoked that I get at Costco.
It's a bargain
but what is most important is that it tastes as good or better than most restaurants.
I also freeze it in six slice sections because it freezes very well with no difference in taste from fresh because of it's high fat content.
That said, this bacon tends to curl.
One thing I realized in my decades of bacon experience is that the bacon, and most food for that matter, tastes much much better when cooked under medium to high heat and in regards to bacon, it lends a beautiful crispy outside and a gentle chewy inside.
Perfect texture!
Bacon press hack:
I found a 5 quart pot that had a footprint that fit perfectly into my nonstick frying pan.
Filled it with a few inches of water so it had some weight, and of course cleaned off the bottom really well, and tried this as a bacon press hack for the first time yesterday.
All I can say is the result was perfect, even, bacon HEAVEN .
In lieu of a dedicated bacon press, this hack works perfectly.
cooking.stackexchange.com/users/62024/InSight
I just make incisions on the fatty rind before frying.
I do however use a press to smooth the creases out of my morning newspaper...
cooking.stackexchange.com/users/18100/freeChampagne
If you are specifically frying them in a pan, I would turn the heat way down, and use a bit more oil.
This cooks like it slowly, so the bacon doesn't curl.
It does however take like, a good 30 mins to cook a strip of bacon.
But you get nice orange color bacon that is ultra crispy.
Cutting the strip in half makes it curl less too.
cooking.stackexchange.com/users/18071/Kasumi
My mother-in-law told me to cover the bacon when you cook it; we use the oven method.
I'm covering the top of the bacon with a piece of foil and will see how that works.
cooking.stackexchange.com/users/21610/user21610
Two ways: Heat the oven to 400 degrees.
Line a baking sheet with sides with parchment paper.
Add the bacon, add a second pan to weigh it down.
No need to turn Second method: Place bacon in a cold skillet.
Add another heavy frying pan over the top.
Fry on low heat, turn after 5 to 8 minutes, turn with tongs, replace the other skillet, and fry until desired doneness: Chewy or crispy.
No need for a press if using another skillet nested into the frying pan.
cooking.stackexchange.com/users/42744/Marilyn Krupa-Burns
If I am pan frying, I cover the bacon with cold water, and cook on medium til the water evaporates.
Then cook until finished.
The bacon cooks evenly and stays flat.
Since I like my bacon extra crisp I will put foil on the bottom of a small pot and press down on the bacon and let it sit for 1 minute or so depending on the cut of bacon.
cooking.stackexchange.com/users/42759/Desiree Kinker
When frying bacon, it tends to curl up. I don't like it because my bacon doesn't cook equally and it's hard to get it crisp that way.  Is there a technique or a tip so I can have flat bacon?
How can I get my bacon flatter?
cooking.stackexchange.com
<frying><bacon><frying-pan>
cooking.stackexchange.com/questions/24069
cooking.stackexchange.com/users/4580/Mien
You can use a bacon press or George Foreman-style grill to flatten it, bake it on a cooling rack to allow the fat to drain away, microwave it, cover it before cooking in the oven or make small incisions in the rind before cooking. Frying at a low heat with more oil will also reduce curling. Try using a bacon press or a George Foreman grill. You can also use the microwave or frying on a lower heat.
Try using a bacon press. Try a George Foreman grill. Try the microwave. Try cooking the bacon on a rack. Try turning down the heat a little. Make incisions in the rind. Cover the bacon as it cooks.