Battlestar Galactica The Resistance - 2006 Webisode 3 1-3 was released on: USA: 12 September 2006
Battlestar Galactica - 2004 Bastille Day 1-3 is rated/received certificates of: Germany:12 Netherlands:12
I don't think it matters. I watched it after I saw season 3 on TV. Since it was released between season 3 and the upcoming season 4 I'd go ahead and watch it after season 3 since that was when it aired.
Battlestar Galactica Razor Flashbacks - 2007 Operation Raptor Talon 1-3 was released on: USA: 19 October 2007 Japan: 25 September 2009 (DVD premiere)
If you have watched the 1980s series, the cylon attack, the mini-series ,season 1, 2 ,3 and later the first and second part of season 4, then that's about it, depending if they go ahead with the movie "the Plan".
The last episode of the remade BSG (2004-2009) was titled, 'Daybreak: Part 3'.
Battlestar Galactica - 1978 Baltar's Escape 1-18 was released on: USA: 11 March 1979 Belgium: 3 June 1981 Netherlands: 22 January 1982 West Germany: 12 July 1989 Hungary: 16 June 2009
Battlestar Galactica - 2004 The Woman King 3-14 was released on: USA: 11 February 2007 UK: 3 April 2007 Spain: 9 May 2007 Germany: 22 February 2008 (limited) Hungary: 30 March 2009 (DVD premiere) Germany: 29 April 2009 Japan: 3 June 2009
Battlestar Galactica - 1978 Lost Planet of the Gods Part 2 1-3 was released on: USA: 1 October 1978 Belgium: 11 March 1981 Netherlands: 30 July 1981 West Germany: 29 March 1989 Hungary: 21 April 2009
Battlestar Galactica - 2004 Crossroads Part 1 3-19 was released on: USA: 18 March 2007 UK: 1 May 2007 Spain: 13 June 2007 Germany: 28 March 2008 (limited) Hungary: 30 March 2009 (DVD premiere) Germany: 3 June 2009 Japan: 8 July 2009
Battlestar Galactica - 2004 A Day in the Life 3-15 was released on: USA: 18 February 2007 UK: 10 April 2007 Spain: 16 May 2007 Germany: 29 February 2008 (limited) Hungary: 30 March 2009 (DVD premiere) Germany: 6 May 2009 Japan: 10 June 2009
The original 1978 series lasted one season, but books continued to expand on the story. The re-imagined series went for 6 Seasons and Included as separate additional films Razor, The Plan, and has a Prequel called Blood & Chrome