This Article discusses the differences between the various Grado pads available, as well as some of the more popular tweaks of these pads.
There are 5 main off-the-shelf pads for the Grado's/Alessandro's headphones:
  1. S-cush "Comfie" Pads
  2. L-Cush "Bowl" Pads
  3. "Flat" Pads
  4. Sennheiser 414 Pads
  5. G-Cush "Jumbo" pads
S-Cush Pads: nicknamed comfies, true to their name, very comfortable, standard on the 60i, 80i and 125i and MS1. These pads allow for an increase in bass, but sacrifice clarity,openness, realism, and some sound-stage.
Quarter-modded Comfies:
This mod makes the comfy pads behave a lot like the TTVJ flats. By opening up the centers, an open chamber is created against the ear for the sound to travel through. simply take a round object (like a quarter), place it in the center of the pad, and cut around it with an exacto knife/razor. the results can be rough in appearence but function just wonderfully. This picture is of Bilavideo's "Quarter modded" pads.
L-Cush "Bowl" Pads:
These are the pads which come stock on the SR-225i and higher headphones. They create a small "donut" shape which sits on top of/around the ear. They leave the driver holes exposed and thus present a more "airy" presentation. By moving the drivers farther from the ears they also create a slightly larger sound-stage, although the sound-stage gains are not incredible, they are evident. By being more open they do however give a presentation that is biased more towards the high-end of the frequency spectrum. The Bowl pads do decrease the amount of bass in relationship to the amount of treble, and as such, those who find the Grado's sibilant already should not consider them. Another problem which many users have with the Bowl pads is that their semi-circum-aural design causes pressure and discomfort on the pinae of the ears that makes long listening sessions less enjoyable and even difficult.
They aren't right for everyone, but for some, especially those with modified Grado's that have stronger bass presence, the bowl pads are an upgrade which provide more realism, clarity, and distance to the music.
Among other places, the L-Cush can be found on Amazon:
"Flat" Pads:
Only TTVJ Audio sells these now as far as I know for $35 USD/pr. They were designed for the vintage Grado such as the HP1000, SR100/200/300 and early RS1. If you put these on any current Grado/Alessandro models, you will experience something similar to the button Bass Boost on old school hifi amplifier. Bass will be very prominent.
Sennheiser 414 Pads:
Although these pads are not made for the Grado headphones, they are a direct fit onto them. These pads are very similar to the "Flat" pads, but are available far more cheaply. The downside is that they are flourescent yellow.
These pads have no center opening, but can be "Quarter Modded" just like the C-Cush pads to provide a more open presentation. The Senn 414 pads can be used either in their normal position, or flipped inside out and installed backwards to provide a smidge more distance between the driver and the ear. (Maverickmonk's Notes: Personally, I love the feeling of the Senn 414 pads, the foam is softer than the standard Grado pads)
To rectify the color, some have dyed their Senn pads, with varying degree's of success. (Maverickmonk's Notes: I used Rit dye and the results were very unsatisfying. Although the pads look wonderful, they now turn my ears black if I listen to them for more than 15 minutes! A higher quality, more permenent dye seeems to be required here)
In conclusion, the Sennheiser 414 pads are a cheap substitute for the Flat pads, they are comfortable, retain bass presence, yet allow a clean presentation, if you can stand the bumble-bee look or can find a method of dying them.
The Senn 414 pads are available to purchase on Amazon:
Sennheiser HD414 pads quartermod
With the quartermods, the HD414 pads are supposed to more closely resemble the flat pads, but due to the consistancy difference, they still are not supposed to be quite the same
G-Cush "Jumbo" Pads
"Modded my SR125 with the G pads. The result was a bigger sound stage and a more wide open feel. On the other hand, because the drivers are further away and there is now "sound pocket" the high frequencies are a tad to bright." - maze400
Some modders glue t-shirt fabric to the inside of their G-cush pads to absorb some of the high-frequency ringing. More info on this mod in the ms1000 thread
All together now (right click "open image in new tab" to see the full size)