Also, folks that played at release but left rather shortly after may be curious what DLC has been patched into the game since release -- what new online modes there are, new cars available, etc.
Beach Bum Content Update(Nov '13)
"It contains 4 beach-themed vehicles, 2 weapons, many new beach-themed clothes (e.g. shorts), 4 new haircuts (2 male and 2 female), new tattoos, and 30+ multiplayer jobs."
Content Creator Update (Dec '13)
"Adds a Map Creator that allows you to make content or 'maps' for Race and Deathmatch modes."
Valentine's Day Massacre Special (Feb '14)
"It includes multiple 1920s mob-styled content: A new weapon (the Gusenberg Sweeper), a new vehicle (the Albany Roosevelt), multiple vintage clothing, a Flapper Bob hairstyle for female characters, a new action in the interaction menu (Blow Kiss), and 10 new jobs."
Content Creator Update #2 (April '14)
"Added Capture mode to the Map Creator."
Business Pack (May '14)
"2 new guns, 4 new vehicles, and lots of new business attire and tattoos."
The High Life Update (May '14)
"1 new gun, 4 new vehicles, and 12 new Jobs. Also added Mental States to MP: your mini-map icon changes colour depending on how passively you play or how aggressively you kill other players; killing an aggressive player is worth more exp."
I'm Not a Hipster Update (June '14)
"2 new weapons, 7 new vehicles, 12 new Jobs, 3 new Gang Attacks, and lots of new 'hipster' clothing and tattoos."
Independence Day Special (July '14)
"2 new guns, 2 new vehicles, 17 new Jobs, and a bunch of holiday themed clothing."
The San Andreas Flight School Update (August '14)
"4 new vehicles, 17 new Jobs, and new parachutes and a flight suit."
The Last Team Standing Update
"2 new guns, 3 new vehicles, 10 new Jobs, and a few new combat themed clothing items. Last Team Standing mode added to the Map Creator."