Gold and Platinum...
  The table below is based on the official RIAA (Recording Industry Association of America) awards, and is probably as accurate as you can get, but it must be borne in mind that any sales figure is open to question - it's not unknown for record companies to sometimes understate sales figures (knowingly or not), the germane example here being Pet Sounds, which is generally regarded as having sold enough to go gold some time in summer 1967. Capitol's reasoning and motives can only be guessed at. One thing must be borne in mind at all times: the record company must request (and pay for) a certification - they aren't awarded automatically.
 
  The current RIAA certification levels are 500,000 units for gold and 1,000,000 units for platinum for singles, and the same figures for albums with additional dollar sales of at least $1 million and $2 million, based on one-third of the list price (although for multi-dics sets, each disc counts towards the award and the dollar sales are not a factor). However, to quote the RIAA, "catalog product, specifically pre-1972 album releases, are eligible for certification by meeting either the unit shipment or manufacturer's dollar requirement for each award level." Translated into English, this means that from 1958-75, the gold qualification for albums was sales of $1,000,000, whereas for a single it was one million units sold. In 1975, the criteria for albums was amended to $1 million in sales at a minimum of 500,000 units sold. The following year the platinum level was introduced, albums being $2 million at 1,000,000 copies, and a straight 2 million copies sold for singles. In 1989 the level for gold singles was reduced to 500,000 copies.  Therefore, although certified gold by the criteria then in place, Endless Summer and "Good Vibrations" would be at least platinum records today (that Endless Summer was on the charts for over three years and only rates gold beggars belief...).
 
The current criteria for DVD/video certification is 50,000 units for gold, 100,000 for platinum.
 
British awards: In the UK, surprisingly, officially ratified awards have only existed since 1973. Less surprisingly, the award levels are somewhat lower, being for singles 400,000 (gold) & 600,000 (platinum), and album being 100,000 (gold) and 300,000 (platinum), Additionally theres a lower award, silver, at 200,000 & 60,000 sales respectively. the UK awards are distinguisehed by a different colored background.
 
Addendum 10/3/03 - Endless Summer  was certified as triple platinum in late September. And about time too...
 
Award date
Level Title
2/18/65
  Gold   All Summer Long
  Beach Boys Concert
10/1/65
  Gold   The Beach Boys Today
11/15/65
  Gold   Surfin' U.S.A.
  Surfer Girl
2/7/66
  Gold   Summer Days (And Summer Nights !!)
12/21/66
  Gold   Little Deuce Coupe
  Shut Down, Volume 2
  Good Vibrations/Let's Go Away For A While
4/12/67
  Gold   Best Of The Beach Boys
8/14/74
  Gold   Endless Summer
10/4/74
  Gold   The Beach Boys In Concert
4/30/75
  Gold   Spirit Of America
7/1/76
  Silver
  Gold
  20 Golden Greats
  20 Golden Greats
8/1/79
  Platinum   20 Golden Greats
9/1/76
  Gold   15 Big Ones
12/10/76
  Gold   Best Of The Beach Boys, Volume 2
1/1/78
  Silver   Holland
  15 Big Ones
2/22/82
  Gold   I Get Around/Don't Worry, Baby
4/6/82
  Gold   The Beach Boys' Christmas Album
7/25/83
  Silver
  Gold
  The Very Best Of The Beach Boys Vol. 1 & 2
  The Very Best Of The Beach Boys Vol. 1 & 2
9/7/83
  Platinum   The Very Best Of The Beach Boys Vol. 1 & 2
5/26/88
  Gold   Made In USA
1/10/89
  Gold
  Platinum
  Kokomo/other artist B side
  Kokomo/other artist B side
11/27/89
  Gold   Still Cruisin'
8/2/90
  Silver
  Gold
  Summer Dreams
  Summer Dreams
9/1/90
  Platinum   Summer Dreams
12/2/91
  Platinum
  Platinum x2
  Best Of The Beach Boys
  Best Of The Beach Boys
2/5/92
  Platinum
  Platinum
  Platinum x2
  Little Deuce Coupe
  Best Of The Beach Boys, Volume 2
  Best Of The Beach Boys, Volume 2
11/2/93
  Gold   Good Vibrations - 30 Years Of the Beach Boys*
6/1/95
  Silver   Best Of The Beach Boys [2CD version]
4/27/99
  Gold
  Platinum
  Platinum x2
  20 Good Vibrations - The Greatest Hits
  20 Good Vibrations - The Greatest Hits
  20 Good Vibrations - The Greatest Hits
2/11/00
  Gold
  Platinum
  Pet Sounds
  Pet Sounds
11/9/01
  Silver   Very Best Of The Beach Boys**
10/25/02
  Gold   Very Best Of The Beach Boys**
9/4/03
  Gold   Sounds Of Summer - The Very Best Of The Beach Boys
9/30/03
  Platinum
  Platinum x2
  Platinum x3
  Platinum
  Platinum x2
  Platinum
  Endless Summer
  Endless Summer
  Endless Summer
  Made In USA
  Made In USA
  Still Cruisin'
5/6/04
  Platinum   Sounds Of Summer - The Very Best Of The Beach Boys
10/01/04
  Silver   Brian Wilson Presents Smile
11/19/04
  Gold   Brian Wilson Presents Smile
6/10/05
  Silver   The Platinum Collection
7/11/05
  Gold
  Platinum
  Brian Wilson Presents Smile [DVD]
  Brian Wilson Presents Smile [DVD]
11/4/05
  Platinum x2   Sounds Of Summer - The Very Best Of The Beach Boys
12/02/05
  Platinum   Very Best Of The Beach Boys**
1/17/08
  Gold   Good Timin' - Live at Knebworth 1980 [DVD]
5/11/12
  Platinum x3   Sounds Of Summer - The Very Best Of The Beach Boys
x
*
 
**
  As noted above, to reach gold certification, this 5CD set had to sell 100,000 units -
  which it did in something under five months. Impressive.
  Not the same collection as the 1983 LPs.