Currently erupting:

Ambrym (Vanuatu): active lava lakes in several craters (updated 16 Sep 2013)
Bagana (Bougainville Island, Papua New Guinea): ash explosions (updated 3 Oct 2013)
Batu Tara (Sunda Islands, Indonesia): strombolian explosions, ash plumes up to 500 m, extrusion of a small lava dome with rockfalls (updated 7 Oct 2013)
Chirinkotan (Northern Kuriles): unspecified activity - possibly lava flows (updated 2 Sep 2013)
Cleveland (Aleutian Islands, Alaska): continuous small eruptions (updated 6 May 2013)
Colima (Western Mexico): lava flow on upper eastern flank (updated 19 Jul 2013)
Dukono (Halmahera): thermal anomaly, probably small explosive activity in summit crater (updated 5 Oct 2013)
Erebus (Antarctica): active lava lake in summit crater (updated 21 Jan 2012)
Erta Ale (Ethiopia): active lava lake in northern pit crater, active hornito with intermittend flow in southern crater (updated 11 Jan 2013)
Fuego (Guatemala): lava flow on upper southern flank, small to moderate explosions (updated 7 Oct 2013)
Grozny (Iturup Island): fumarolic activity (updated 3 Apr 2013)
Jebel Zubair (Red Sea): submarine eruption started 28 Sep 2013 (updated 2 Oct 2013)
Karkar (Northeast of New Guinea): possible ash eruption on 1 February (updated 15 Mar 2013)
Karymsky (Kamchatka): occasional small explosions, thermal anomaly (updated 7 Oct 2013)
Kilauea (Hawai'i): lava lakes in Halemau'uma'u and Pu'u 'O'o, lava flows on coastal flat and weakly active ocean entries (updated 13 Aug 2013)
Kizimen (Kamchatka): growing lava dome and incandescent rock avalanches (updated 1 Oct 2013)
Klyuchevskoy (Kamchatka): strombolian activity at summit crater (updated 7 Oct 2013)
Marapi (Western Sumatra, Indonesia): occasional weak explosions (updated 14 Aug 2013)
Nyiragongo (DRCongo): active lava lake in summit crater (updated 12 Jun 2013)
Ol Doinyo Lengai (Tanzania): effusion of natrocarbonatite lava inside the crater (updated 8 Jul 2013)
Pacaya (Guatemala): strombolian activity and lava flow (updated 5 Oct 2013)
Paluweh (off Flores Island, Indonesia): active growing lava dome (updated 12 Aug 2013)
Rabaul (Tavurvur) (New Britain, Papua New Guinea): explosions and ash emissions (updated 1 Oct 2013)
Rausu (Hokkaido)
Reventador (Ecuador): ash explosions, occasional pyroclastic flows (updated 9 Oct 2013)
Sakurajima (Kyushu, Japan): constant ash emissions and strong explosions (updated 9 Oct 2013)
Santa María / Santiaguito (Guatemala): Santiaguito volcano (Guatemala): lava flow on south flank of dome becomes more active (updated 5 Oct 2013)
Semeru (East Java, Indonesia): growing lava dome, ash venting and small to moderate explosions (updated 25 Jul 2012)
Shiveluch (Kamchatka): slow dome growth, occasional explosions and pyroclastic flows (updated 1 Oct 2013)
Stromboli (Eolian Islands, Italy): continuing lava overflows (updated 25 Jul 2013)
Suwanose-jima (Ryukyu Islands): Mt Ontake volcano of Suwanose-jima Island, Japan (updated 12 Sep 2013)
Telica (Nicaragua): normal (low) seismic activity (updated 26 Sep 2013)
Tinakula (Santa Cruz Islands, Solomon Islands): increased activity at the volcano (updated 8 Feb 2013)
Tungurahua (Ecuador): degassing, earthquake swarm and inflation (updated 9 Oct 2013)
Ulawun (New Britain, Papua New Guinea): steaming, degassing (updated 1 Oct 2013)
Veniaminof (Alaska Peninsula, USA): effusion of lava flows (updated 6 Oct 2013)
Yasur (Tanna Island, Vanuatu): strong strombolian activity (level 3), crater currently closed (updated 10 Sep 2013)

Eruption warning / minor activity:

Bezymianny (Central Kamchatka Depression): slow lava flow extrusion from dome (updated 1 Oct 2013)
Dieng (Central Java): increased degassing (updated 28 Mar 2013)
Etna (Sicily, Italy): sporadic ash emissions from New SE crater (updated 6 Oct 2013)
Galeras (Colombia): sporadic ash emissions (updated 25 Jul 2013)
Gamkonora (Halmahera): seismic swam, minor ash emissions (updated 27 May 2013)
Heard (Australia, Southern Indian Ocean): likely lava lake in summit crater (updated 3 Oct 2013)
Ibu (Halmahera, Indonesia): growing lava dome, seismic unrest (updated 9 Jun 2013)
Iliwerung (Lesser Sunda Islands): possible submarine eruption from Mt Hobal on 20 August (updated 20 Aug 2013)
Iwo-Tori-shima (Ryukyu Islands): possible small ash eruption on 6 July 2013 (updated 6 Jul 2013)
Karangetang (Siau Island, Sangihe Islands, Indonesia): lava extrusion at summit crater, strombolian activity, glowing avalanches (updated 4 Sep 2013)
Kerinci (Sumatra): occasional ash explosions (updated 5 Jun 2013)
Ketoi (Kurile Islands, Russia)
Kikai (Ryukyu Islands): steaming at summit crater of Iodake, occasional weak glows (updated 5 Jun 2013)
Kirishima (Kyushu): degassing, slightly increased seismic activity (updated 30 Jul 2012)
Langila (New Britain, Papua New Guinea): occasional ash explosions (updated 11 Feb 2013)
Lokon-Empung (North Sulawesi, Indonesia): small explosions, lava flow? (updated 24 Sep 2013)
Manam (Papua New Guinea): occasional explosions (updated 12 Sep 2013)
Medvezhia (Kurile Islands, Russia): strong steaming, thermal anomaly (updated 17 Jan 2013)
Merapi (Central Java): moderate gas and ash plume on 22 july (updated 3 Oct 2013)
Nevado del Ruiz (Colombia): seismic unrest (updated 7 Oct 2013)
Nyamuragira (DRCongo): steaming/degassing from pit inside summit caldera (updated 18 Jul 2013)
Papandayan (West Java): strong hydrothermal activity, increased seismicity (updated 6 May 2013)
Poas (Costa Rica): occasional small phreatic explosions from lake (updated 22 Aug 2013)
Popocatépetl (Central Mexico): steam/gas/ash emissions (updated 5 Oct 2013)
Rasshua (Central Kuriles)
Raung (East Java): strombolian activity in summit crater (updated 5 Aug 2013)
Rincón de la Vieja (Costa Rica): small phreatic eruption on 11 April (updated 6 Oct 2012)
Sacabaya (Northern Chile, Bolivia and Argentina)
Tangkubanparahu (West Java): occasional phreatic explosions (updated 7 Oct 2013)
Turrialba (Costa Rica): ash venting, strong degassing (updated 24 Jul 2013)
Ubinas (Peru): occasional phreatic explosions (updated 20 Sep 2013)