You have reviewed various programs/apps that can help GMing; how about a compiled list of “Apps for your mobile device you must have,” or “Tiny proto-robot makes killing PCs easier (I jest).” Most people have some kind of smart phone these days and not everyone wants to bring their laptop.
It would be nice if the list was not iPhone-centric.
I’m not sure if we can make you an exhaustive list, but we can definitely send our little gnome-bots out to scour the interwebs, kill halflings, and report back the best that we find. Oh look, the gnome-bots are returning already caked in blood.
- Adobe Reader – Any Device – PDFs, legal or not , are a big part of the current gaming landscape. You want to be able to read them reliably with your mobile device.
Update: snej mentions that GoodReader  is the PDF reader of note for the iPhone.
- Filemagnet – iPhone – Can help ease some of the issues of transferring files to your iPhone.
- Tapatalk – iPhone – A forum reader for the iPhone. Take enWorld with you and debate which system is better from anywhere! (I kid, I kid!)
- NPC NAMER – iPhone – Need Names? Course you do.
Apps, Apps, Apps
- Pocket Tabletop Rpg Helper – Android – Contains a die roller and tracking programs for Guprs, D&D, Shadworun, and WoD.
- Tinwatchman Initiative Tracker – All (HTML)– An initiative tracker for multiple types of systems.
- Scryer – All (HTML) – Justin Kohlhepp. developed a nifty little webpage that searches the D&D Compendium API to
- D&D 3.5 Treasure Roller – Pocket PC – A nifty little treasure roller for the 3.5 crowd.
- The WFRP Toolkit – iPhone - For all you Warhammer Fantasy Gamers out there.
- The 3.5e Fantasy RPG Experience Calculator – iPhone – Ever tire of figuring out the arcane formulae for experience in 3.5. We all do. This will have you jumping for joy.
- The Dungeon Master’s Toolkit – iPhone – Made for multiple fantasy games, this one looks pretty and seems to have lots of features.
- D20 Ability Calculator – Android – A fairly basic character ability calculator.
http://www.androidzoom.com/android_applications/tools/d20-ability-calculator_bfoz.html  
- Worldbuilder – iPhone – Lots of tools for building and tracking worlds on the fly.
- GM Toolkit – iPhone – Die rolling, Name Gen, Room Gen, Place Name Gen, all the basic things GMs need help with from time to time. http://itunes.apple.com/us/app/gmtoolkit-rpg-helper/id320133589?mt=8 
Web Pages That Work Well On A Mobile Site
- The Player Side of Screen Monkey – All (HTML) – The player side of Screen Monkey can be accessed over the world wide web. One GM with a laptop, players with mobile devices. The day has come.
- Sounddogs – All (HTML)– Using the preview sounds you can get lots of real quick music or sound effects right on your mobile device. YMMV depending on how your device handles the playing of MP3s from links.
-  Pathfinder Mobile SRD – All (HTML)– Play pathfinder? Want access to the SRD from your phone? Here ya go:
- Online Name Generator – All (HTML) – Not sure how well the page will look on a small screen, but the big buttons for generating names and the variety might make this a good choice.
Wow there are a lot out there, want more? Try these sites
The Gnome-bots got tired trying to find all of best apps out there. While I picked the best apps I could find based off of reviews and forum posts, there were a whole lot more out there. Want some good search tools? Try these sites:
- iPhone App Store Search for RPG – http://www.uquery.com/search?q=rpg&commit=Search 
- A Great Forum Thread by Morrus that shows many apps –
- Androlib Search for RPG – http://www.androlib.com/r.aspx?r=RPG&p=7 
- Paizo Forum Post About Mobile Apps – http://paizo.com/paizo/messageboards/paizoPublishing/pathfinder/pathfinderRPG/general/itouchIphoneAppsForPathfinderAndOtherTabletopRPG 
So, what essential apps have I missed? What would be the “Killer App” that you want to see on a mobile device? Are you in fact reading Gnome Stew on a mobile phone right now? Freaky.
Gnome Robot Image: Here  – CC-BY-NC-SA
Other Images: Used for illustrative purposes.