I really love Urban Decay Ink For Eyes. The packaging is so much cleaner and neater and efficient than most. At least for the way I use it on others. They offer it in the five standard colours, plus a clear base with rainbow glitter in it that I use in just about any way but eyeliner. I really love that stuff.
However, if you need more avant-garde kind of stuff, the Make Up For Ever Aqua Cream is excellent. It's a multi-use product that works perfectly as a gel liner or a base, and it's flexible and crease resistant, which is really all you would need out of it, right? I believe it comes in almost two dozen colours [basically everything but black, which is weird] including red, and orange, and several shades of pink and blue and neutrals. It works great as a liner with a razor thin angled brush, and it dries great, but I always am tempted to layer a matching shadow or translucent powder over it out of paranoia, and I know that works BEAUTIFULLY and it doesn't go anywhere. I don't imagine it would make a huge difference without it, though.
There's also the MUFE Aquarelle which almost all shades of can be used as an eyeliner. It's more of a liquid but it's packaged in a sanitary vial so it's just as safe to use on multiple people as a pot you can scrape out of. You can also use it to draw on people with, if that is a selling point to you.