These are some goodies that I've tacked onto my printers. They're mostly applicable to Ender 3's and Ender 5's, so be sure to check for the right model for your particular printer!
BL Touch (v3.1)
Bed Leveling Begone! (almost)
A frequent pet-peeve with printing is having to deal with leveling the bed. The BL Touch is a frequently recommended probe for the Creality Ender printers. In layman's terms, it's a sensor makes use of a plunger and a (hall effect) sensor together to determine the minute differences in proximity between where the bed and the probe is. It creates a mesh of the surface of the bed, and then alters the z-movement of the nozzle ever so slightly for a consistent print.
Vinh's Thoughts: I put a BL Touch on every Creality printer I own. Even the Ender 3 V2 I bought out-the-box, I immediately slapped on the BL Touch. You will still have to level your bed manually, though the sensor will help you address slightly uneven parts of your bed surface.
45$ USD (as of 8/27/2021)
Flat Yellow Springs
Stiffer bed springs prevent your bed from de-leveling
So you spent a LONG time getting your bed leveled, and after printing for a few months of knocking prints off while the bed is hot (don't do this!), you come to your office and find that the screws that hold the bed level have come off, and your print is ruined!
Stiffer bed springs, like these yellow ones, can help prevent this. These would keep more tension between the leveling wheel and the bed, and helps your bed remain level for longer.
Vinh's Thoughts: You'll need these eventually.
10$ USD (as of 8/27/2021)
Aluminum Extruder Assembly
Either an essential or an aesthetic upgrade.
An essential enhancement if your printer has a extruder assembly without brass inserts for its input and output of the nozzle. Otherwise, a great aesthetic enhancement. You'd only need this if your printer has an older extruder without a brass hole for filament to pass through. The reason being is that after a few miles of filament passing through, it will literally cut through the plastic very slowly, eroding the extruder arm away.
Vinh's Thoughts: I upgrade every printer I have to have an aluminum extruder assembly.
45$ USD (as of 8/27/2021)
Amazon - Combo with the Capricorn Bowden PTFE Tubing! 25$
Capricorn Bowden PTFE Tubing
Tight tolerances and better heat tolerance
One of the pros of this particular tubing is its tighter tolerances, which let you print flexible materials easier. While I don't usually recommend printing anything below 95A shore, the tubing does come in handy for better temperature resilience for when you upgrade to a all-metal hot-end and find yourself printing materials above 250 C.
You'll price yourself out of lower quality filament with this tubing too- some lower quality filament isn't exactly 1.5mm in diameter, or may have rough texturing which causes to bind inside this tube.
Vinh's Thoughts: I've fitted every one of my printers with this upgraded tubing.
15$ USD (as of 8/27/2021)
Amazon - Combo with an aluminum extruder set! 25$
Swiss Micro All Metal Hot End
For when you want to get hotter
This upgrade is essential if you want to print something other than PLA- especially materials that require anything beyond 250 C like nylon or polycarbonate (PC).
If you're just printing PLA and PLA+, I wouldn't get this upgrade, as you'll have to reduce the retractions you can do. The reason being is that retractions will pull molten plastic up into the heatsink, which will cause it to gob up and stick to the stainless steel walls. It's a big pain! (This is an issue related to heat creep, since an all-metal hot-end conducts heat easier.)
Don't forget to do a PID calibration after you replace your hot-end with this one, along with making sure your firmware supports going over 250 C with the appropriate thermoresistor.
Vinh's Thoughts: You'll have to tweak your heating settings to run slightly hotter, and lower (or disable retraction!) in your profile with this upgrade. For printing in nylon or PC, this is an essential upgrade.
65$ USD (as of 10/21/2021)
Swiss Micro NG Extruder
For when you want to print softer and hotter
(This replaces my previous recommendation of the "Swiss Micro Direct Drive Extruder & All Metal Hot End." It's a recent release from Swiss Micro and in my opinion is superior to the former in every way.)
Most people don't need a direct drive extruder, but it's needed if they want to print softer, more malleable materials, like TPU. The improvement over the old Direct Drive Extruder is the much lighter LDO stepper motor, along with the tighter distance between the gears and the nozzle. (This reduces the chance of softer materials binding and getting stuck in the gears.)
This is a great pairing for an Ender 3 V2 upgrade. The instructions are simple, and easy to follow from Micro Swiss' website. The steps are involved, but can move quickly if you are used to tinkering with your printer. You only need to attach your fans (and it uses the same ones!), along with your bed leveling sensor (which you need to print the mount before you start). After which, you adjust your Z-steps and go from there with recalibration and bed leveling.
For added value, buying this also nabs you the all metal hot-end.
Vinh's Thoughts: This upgrade is a win in my book. It's easy to put together, and is good value for what you get out of it.
120$ USD (as of 9/14/2023)
Hardened Steel Nozzle
For more abrasive materials (or if you're lazy)
Brass is a soft metal, so it will eventually wear out if you print a lot. With a steel nozzle, you'll go much longer without having to replace your nozzle.
A harder nozzle is also required if you're printing in more abrasive materials, like nylon or with glow-in-the-dark filament. These filaments will widen the opening on your brass nozzles in no time.
Vinh's Thoughts: I'm lazy so I bought this and swapped out my brass nozzles once they wore out.
10$ USD (as of 10/21/2021)
APC UPS Battery Backup and Surge Protector
Save your prints and your equipment
As with all hi-tech stuff, it's good practice to put it behind a surge protector (and ideally a battery backup). But for 3D printers- the need for a battery backup becomes very evident: you don't want your prints getting derailed and restarted after a small power blip.
Even if your printer has a "power-off resume function", this doesn't necessarily work all that well. Some printers will skip that layer height, creating a gap in your print. Other times, the nozzle may cool and get stuck to your print where it is (so then when you go to move your nozzle, your print detaches). It's better to just not let the power go off in the first place. If you are using OctoPi, forget about this feature saving your print.
I have a 650VA on three of my Ender 3's running a silent board (which has better power consumption), but if you have just one Ender 3, 650VA is perfect for that and an OctoPi.
Vinh's Thoughts: If your power goes out infrequently, or if you print anything that's at least a day long, this will pay for itself in a few rolls of filament.
65$ USD (as of 11/18/2021) for the 650VA
Tiny Machines 3D's Z Sync Kit for CR Series Printers
Only for CR-10's
This is a must have if you have a CR-10, or a CR-10 based printer. It keeps your gantry level when the power is disconnected, and discourages striking or turning one stepper without the other.
Vinh's Thoughts: I have rescued two CR-10's and a Weedo X40 with this kit. It's inexpensive, and saves headaches later on.
15$ USD (as of 9/14/2023)