$$$ - paid apk

demo - ads, limited version or both

Virtual tabletop

https://play.google.com/store/apps/details?id=com.YogurtForFun.SkCombat

https://play.google.com/store/apps/details?id=com.taponfire.threedvirtualtabletop

General help (usually "Swiss army knives", aka toolkits featuring dice rollers, charsheets, maps etc)

https://play.google.com/store/apps/details?id=air.com.goatheadsoftware.dmminionpf (4 toolkit apks for DnD & PFRPG, free + $$$ versions)

https://play.google.com/store/apps/details?id=com.pingdevelopment.gmtoolkit (toolkit, awful looking, but useful)

https://play.google.com/store/apps/details?id=com.zalzala.gmscreen (DM screen, DnD 3.5)

https://play.google.com/store/apps/details?id=com.lateensoft.pathfinder.toolkit (toolkit, PFRPG)

https://play.google.com/store/apps/details?id=com.climbwalls.pgm ($$$, toolkit, general)

https://play.google.com/store/apps/details?id=com.climbwalls.pgmd (same as above, demo)

https://play.google.com/store/apps/details?id=com.xalops.archivist.elements (Toolkit, general)

https://play.google.com/store/apps/details?id=com.dragaoboreal.tabletopsquire ($$$, toolkit)

https://play.google.com/store/apps/details?id=com.dragaoboreal.tabletopsquire (Toolkit, D20, GURPS, Shadowrun, WoD).

https://play.google.com/store/apps/details?id=com.v1_4.B7132B97252BEE808EF4B47E.com ($$$ general, D20 oriented)

https://play.google.com/store/apps/details?id=com.bullercodeworks.gamekeeper ($$$ toolkit, general)

https://play.google.com/store/apps/details?id=com.bullercodeworks.gamekeeper_free (same as above, demo)

https://play.google.com/store/apps/details?id=com.DungeonsandDragons ($$$, D&D)

Mapmakers

https://play.google.com/store/apps/details?id=air.com.thinkingimpairedstudios.yeoldemapmaker ($$$, Mapmaker, costly, but good)

https://play.google.com/store/apps/details?id=com.tbocek.android.combatmap (Mapmaker)

https://play.google.com/store/apps/details?id=pl.planmieszkania.android (floor plans designer)

https://play.google.com/store/apps/details?id=com.anadreline.android.madrees (floor plans designer)

https://play.google.com/store/apps/details?id=com.nvc.familyhomeplans (houses, floor plans)

Dice

https://play.google.com/store/apps/details?id=com.droidhut.dicebag

https://play.google.com/store/apps/details?id=com.cyancanyon.aleatori

https://play.google.com/store/apps/details?id=com.rambutan.dice

https://play.google.com/store/apps/details?id=ohm.quickdice

https://play.google.com/store/apps/details?id=com.bullercodeworks.gamekeeper ($$$, very advanced)

https://play.google.com/store/apps/details?id=com.bullercodeworks.gamekeeper_free (same as above, demo)

https://play.google.com/store/apps/details?id=com.pallosalama.dice.dnd ($$$, visual)

https://play.google.com/store/apps/details?id=com.rb.swdr (SAVAGE WORLDS)

Compendium

https://play.google.com/store/apps/details?id=org.evilsoft.pathfinder.reference (wonderful apk! PFRPG)

https://play.google.com/store/apps/details?id=com.dragora.pfsrd ($$$, PFRPG)

https://play.google.com/store/apps/details?id=com.androidbok.myfirstresourcetesterapp (PFRPG)

https://play.google.com/store/apps/details?id=air.be.jonsson.pathfinder.feat.talent.compendium (feats PFRPG)

https://play.google.com/store/apps/details?id=com.vansteinengroentjes.apps.ddcompletereference (3,5)

https://play.google.com/store/apps/details?id=com.jellware.dndsheet (3,5)

https://play.google.com/store/apps/details?id=com.ryatziv (DnD 4)

https://play.google.com/store/apps/details?id=com.slovenlyimp.sylloge ($$$, DnD 4)

Spells:

https://play.google.com/store/apps/details?id=air.be.jonsson.pathfinder.compendium (PFRPG)

https://play.google.com/store/apps/details?id=com.ChicaneryGames.PathfindersSpellbook (PFRPG)

https://play.google.com/store/apps/details?id=com.zalzala.spellbookpf ($$$, nice looking, PFRPG)

https://play.google.com/store/apps/details?id=com.zalzala.spellbook (DnD 3.5)

Character sheets & Generators

https://play.google.com/store/apps/details?id=com.dysfunctional.apps.pcgencharactersheet (PFRPG)

https://play.google.com/store/apps/details?id=com.dysfunctional.apps.pcgencharactersheetlite (same as above, ads)

https://play.google.com/store/apps/details?id=com.prometheusapps.pathfindercharactersheet (PFRPG)

https://play.google.com/store/apps/details?id=com.thomasgallinari.dndcharactersheet (DnD 4)

https://play.google.com/store/apps/details?id=evan.curtis.char_sheet (DnD 3.5)

https://play.google.com/store/apps/details?id=com.android.ash.charactersheet ($$$, DnD 3.5+PFRPG)

https://play.google.com/store/apps/details?id=bidalaka.dnd (DnD 2.0)

https://play.google.com/store/apps/details?id=com.silfer.cochelperPaid ($$$, Call of Cthulhu)

https://play.google.com/store/apps/details?id=com.silfer.cochelper (same as above, demo)

https://play.google.com/store/apps/details?id=com.ytang.cocchargen (Call of Cthulhu)

NPCs:

https://play.google.com/store/apps/details?id=com.zalzala.pfnpc (PFRPG)

https://play.google.com/store/apps/details?id=com.acarcana.RPGCharacterBackgroundGenerator (General, D20 oriented)

https://play.google.com/store/apps/details?id=air.npcgenerator (General, D20 oriented)

https://play.google.com/store/apps/details?id=com.blank.bestiary (PFRPG monsters)

Other

https://play.google.com/store/apps/details?id=com.axehigh.rpg.encounters (random encounters)

https://play.google.com/store/apps/details?id=com.ixc.Syrinscape (sound creator)

https://play.google.com/store/apps/details?id=com.dragaoboreal.songsanddragons ("atmosphere" assistant - music, scenes, etc)

https://play.google.com/store/apps/details?id=com.Devend.AdventureGeneratorPro (adventure generator)

https://play.google.com/store/apps/details?id=com.dungen (dungeon generator)

https://play.google.com/store/apps/details?id=com.axehigh.rpg.encounters (500-800 fantasy encounter ideas)

https://play.google.com/store/apps/details?id=com.pathfinderindex.layingwaste ($$$ critical hits generator, PFRPG)

https://play.google.com/store/apps/details?id=net.battlescribe.rostereditorpro ($$$ army creator)

https://play.google.com/store/apps/details?id=net.battlescribe.rostereditor (same as above, demo)

https://play.google.com/store/apps/details?id=me.cmrn.squire (combat assistant, general)

https://play.google.com/store/apps/details?id=com.roseburner.swctbeta (combat assistant, SAVAGE WORLDS)

https://play.google.com/store/apps/details?id=org.visionsoftware.combatassistant ($$$, combat assistant, DnD 4)

https://play.google.com/store/apps/details?id=org.visionsoftware.combatassistantfree (same as above, demo)

https://play.google.com/store/apps/details?id=com.dragora.pfbattle ($$$, combat assitant, PFRPG)

https://play.google.com/store/apps/details?id=com.dragora.lite.pfbattle (same as above, demo)

https://play.google.com/store/apps/details?id=com.dragora.summonerpftot ($$$, summoner assitant, PFRPG)

https://play.google.com/store/apps/details?id=com.dragora.summonerpf (same as above, demo)

https://play.google.com/store/apps/details?id=de.delusions.rpgtracker (HP Tracker)

https://play.google.com/store/apps/details?id=com.pterodattilo.backpack (backpack simulator)

https://play.google.com/store/apps/details?id=com.spellstwoed.main (DnD 2.0 spellbook)

Supporting applications

https://play.google.com/store/apps/details?id=com.foobnix.pro.pdf.reader&hl=en ($$$, probably fastest PDF reader)

https://play.google.com/store/apps/details?id=com.foobnix.pdf.reader&hl=en (same as above, demo)

https://play.google.com/store/apps/details?id=com.branchfire.iannotate&hl=en (PDF reader supporting multiple PDFs in tabs)

https://play.google.com/store/apps/details?id=com.mediafire.android (Mediafire official application)