With the industry shifting to using foam rubber for prosthesis there are a plethora of different styles out there now. Foam rubber breathes while latex does not. Much more comfortable for extended wear. Plus if you want something a bit more dramatic than the typical 'spock' type of elf ears, I've seen the WoW night-elf style 'antenna' ears out there.
As far as adhesives go, I personally prefer 'medical adhesive' as it provides a much more resilient hold and doesn't sweat off or dry out and crack like spirit gum does. The trick is to paint it on where you want it sticky and then let it dry before you apply the mask/ears/nose/etc. If you want something to stay put for a LONG time or it's something that's likely to take some abuse, dont let the adhesive dry before you put it on. Be forewarned that you might need remover to get it back off when you're done tho!

LC Sullivan
Omega Reef Marines
Omega Prime
Imperial Mercenaries Guild/Archonium
Military Union Commander, Asylum branch
To secure peace: Prepare for war.
If someone tries to kill you, you kill them right back.
Sometimes a sword is better left unused.