That's a big question with a long answer, I'll try to do an abbreviated answer. There were a few iterations in the early years like the Disc Glide and FXRC, but from about '87 on the line didn't change much.
FXR- ('82+) The base model, known as the Superglide, eventually had speedo on tank and buckhorn handlebars.
FXRS ('82+) a little more bling than the FXR, it became the Lowrider. In '88 tach and speedo were moved from the bars to the tank.
FXRDG Disc Glide, similar to FXRS with solid disc rear wheel. '84 only I think.
FXRC - The C is for "custom" and ran from '85 to '87, these were basically FXRS's with more chrome and special paint. The '85 was called the ''candy glide" because of the tangerine paint and brown seat, '87 had blue and black paint with a blue frame.
FXRS-SP Low Rider Sport - In '87 these added dual disc front brakes, taller suspension, low bars, and a smooth seat, bar mounted tach/speedo to the FXRS. '88+ had anti dive air forks.
FXLR Low Rider Custom - Released in '87 and had a disc rear wheel, 21' spoke front wheel, no tank console, and unique pull back drag bars which held the speedo.
FXRS-Conv Low Rider Convertible '89+, was an -SP with detachable windshield and bags, along with buckhorn handlebars, sissy bar, pillow seat, and I believe hi way pegs.
FXRT - '84+ had fairing and hard bags.
FXRD - '86 ONLY, It was an upscale FXRT and added a top case, unique exhaust with a pipe on both sides. Rare
FXRP - Police bike, based on the FXRT but different fairing and bags, seat, etc.
The Dyna came out in '91 with the all black Sturgis, in '92 they added the Daytona and Custom. In '93 the FXRS Low Rider was replaced by the Dyna Low Rider and by '95 all the FXR's were gone and replaced by Dynas.
I think there's a more detailed timeline on the CVO Harley forum posted by Classicrider.
