I use an
amp opener because it it small and portable. A triangle file works fine though.
Some guys recommend just putting a pen cap over the top and snapping it but there are certain amps that I assure you will not work with this method. ICN are the hardest I've come across to open cleanly.
Here are some addys of places that sell
amp openers.
www.androusa.com (They have disposable ones that I have never used so can't comment on them. They used to have a good one but don't carry it anymore.)
http://www.hcl-intl.com/products/mall/pharmacy/7371.asp (I have used this type. . .good stuff)
I had some more sites but I can't find them. Try a search on yahoo.
Peace. Freez.