Here's some links to help you find out more about Monsterweights.
I am not affiliated with or paid by any of the companies I have listed. I list them only to spead the word of their greatness!

Please take the time to review these links. They have many people's opinions and experiences with heavy valve caps.

Favorite Tuba sites
Sean Chisham's Tubenet What a resource for links, chat, and research! Sean has it all.
The Tubastore Where to find Charlie Krause, and Brook Mays, one of the best places to buy a tuba in the world!
ITEA (formerly TUBA) the homepage for ITEA, also has links to international conventions.
Dillon Music Dillon Music are brass specialists out of New Jersey. They have everything, including a great selection of used instuments, with pictures.

Links with information about heavy caps
Curry Ccaps for trumpet The makers of the most popular Heavyweight caps for trumpet in the world!
Description of monette valve caps Talks about properties of heavy caps and their effect on playing.
Report about tuba caps Report from someone who I inspired to make his own caps. Includes detailed effects on the changes they cause.

Rather long thread with many details about the effects of heavy weights worth every click. Great information!
Great article on Trumpet Caps Be sure to place a description of your link for your viewers here!
Aftermarket product review on Curry caps user review on Ccaps
Charlie Krause's story of the effects on a miraphone 191 this is the post that really got people excited about my product!

One more for the skeptics go to Google and type Heavy weight valve caps. I could not find anything but positives.