There are various tens pads out there. Various people will recommend various ones.
If there are any specific ones I have used they will be listed here. I don't know about other kinds.
Tens toys can be used with all the boxes like Folsom, PES and Eros-tek.
However, toys used with them should not be used above the waist.
Click here to see information on adapters.

VITATRODE TENS PADS: these are really soft & gooey. The oval (1.5"x 2.5") were recommended to me as good for placing on the clit. They work well for that, but they can slide around a bit like all other pads.
These can be purchased at VitalityWeb.

CARBON RUBBER PADS: There are a variety of different sizes & styles in these. They don't stick on there own, you need some kind of gel. Though it is nice that they are durable and reusable pretty much forever, I haven't gotten them to stick or conduct as well because of that overall. If you need to have something washable that can be used on more than one person, getting a set of these is a good idea. These are also available at VitalityWeb.

BREAST SHIELD: I really don't know anything about these other than they exist and I would like to try them sometime. It is obviouly meant for above the waist play so it may not be suitable for use on some people. You use it at your own risk. They can be purchased at: Affortable Bondage Gear.