Was looking for this and couldn't find it, so summarized it here (from Lexus CPO website). If there are any changes/corrections, please post them here.

Thanks

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1999

Introduced in the spring of 1998 as a 1999 model, the RX 300 was the new car-based sport-utility vehicle for Lexus.

2000

Introduced in 1999, the RX 300 combines the ruggedness of an SUV with the comfortable ride of a car. The 2000 Lexus RX 300 retains virtually all the standard features of the original model. With elegance in design, in addition to advanced engineering systems, it achieves the perfect balance between adventure and drivability.

The 2000 model maintains the uniquely contoured lines, but exterior color Mineral Green Opalescent replaces Desert Bronze Metallic. Some models may also be available with a new factory rear spoiler.

2001

For 2001 Lexus adds some significant enhancements such as a more elegant front grille, Vehicle Skid Control (VSC) and Brake Assist. A DVD-based, touchscreen navigation system is now available. With elegance in design, in addition to advanced engineering systems, the RX 300 achieves the perfect balance between adventure and drivability.

The 2001 model maintains the uniquely contoured lines, but exterior colors White Gold Crystal, Sunset Mist Pearl, Indigo Ink Pearl and Blue Vapor Metallic replace Golden Pearl, Venetian Red Pearl and Twilight Blue Pearl.

Changes Made To The 2001 RX 300

Standard Features:

- More luxurious front grille, headlamps and rear combination lamps

note: the 'Altezza style' tail lamp cluster started in 2001

- Larger fuel tank
- Brake Assist
- Water-repellent front-door glass
- Rear bumper protector
- Chrome inside door handles
- New seat fabric
- Vehicle Skid Control (VSC)
- Heated outside mirrors with water-repellent film
- Lexus chrome scuff plates
- Updated ivory-colored fabric seats
- Improved visibility on multi-information screen
- Additional rear cupholder
- Three-point seatbelts for all seating positions
- Rear outboard child-seat tether anchors
- Collision fuel cutoff

Optional Features:

- Lexus Chrome Wheels
- High-Intensity Discharge (HID) headlights
- New exterior colors White Gold Crystal, Sunset Mist Pearl, Indigo Ink Pearl and Blue Vapor Metallic replace Golden Pearl, Venetian Red Pearl and Twilight Blue Pearl
- Leather trim now available in black
- Wood- and leather-trimmed steering wheel and shift ****
- Coat hooks
- Dual-setting heated seats
- Touchscreen Lexus DVD Navigation System
- Compass

2002

No changes from 2001

2003

The 2003 RX 300 offers the best of both worlds--the ample room of an SUV and the effortless ride of a luxury sedan. You can relax even more knowing that the RX comes with an array of safety features, including Brake Assist, rear outboard Child Restraint Seat tether anchors and Vehicle Skid Control.

For 2003, the RX's power tilt-and-slide moonroof with one-touch open/close and sliding sunshade is now standard.

Changes Made To The 2003 RX 300

Standard Features:

- Power tilt-and-slide moonroof with one-touch open/close, and sliding sunshade

2004 -- NEW MODEL

RX330

The all-new 2004 RX 330 sets a new standard for luxury utility vehicles. Combining remarkable technology, sophisticated styling and exceptional luxury, the RX provides an unforgettable driving experience.

The RX's state-of-the-art technology takes safety, convenience and luxury features to a whole new level. An available Backup Camera now makes it possible to see what's behind your vehicle when you back up. When you're moving forward, the RX's available Dynamic Laser Cruise Control adjusts your speed to maintain a pre-set following distance. The RX even adjusts to rainfall, with available Rain-Sensing Intermittent Windshield Wipers. Advanced safety features include a front seat-mounted side airbag with a larger protection area than a conventional side airbag, a driver's multistage Supplemental Restraint System which deploys the airbag in one of three speeds, and a driver's knee airbag.

And while entertaining yourself by driving the RX, passengers can enjoy themselves with an available Lexus DVD Rear-Seat Entertainment System. If you're carrying cargo instead of passengers, you'll appreciate the available power rear door with remote keyless entry.

With such an innovative luxury utility vehicle as the RX 330, you may find yourself inventing new reasons to take it for a drive.

 

from Lexus website...

The Special-Edition RX 300 Silversport: Impresses Woodland Creatures And Nightclub Bouncers

December 1, 2000, Torrance, Calif. -- With a Silversport grille and an interior trimmed with brushed aluminum and Black perforated leather, Lexus is pleased to provide you with the opportunity to pronounce your active lifestyle. Available with a monotone Black or Silver exterior, the RX 300 Silversport features a Euro-tuned Suspension, silver-finished CrossBars and special Black Pearl badging to distinguish itself from the masses. The Silversport is only available as a 2001 RX 300 model.

 

From the sticker sheet:

Coach Special Edition with navigation system: $7345.00

- Coach Leather Trim Seats with perforated inserts
- Coach logo embossed on headrests
- Bird's Eye maple trim (including steering wheel)
- special floormats with Coach logo
- Coach "Hampton" Cabin Bag and Demi-Pouch,
- color coordinated bumpers and cladding,
- Coach "honeycomb" front grille, polished wheels,
- Coach badge on front doors,
- one-touch open/close moonroof,
- in-dash 6 CD changer,
- interior air filter,
- electrochromic (automatic dimming/adjusting) mirrors

 

Are the following available for earlier model (1999-2000) RX300 ??
- HID
- DVD NAV system

 

Sometime in the late 1999 models, and on all 2000 models, the heated seat button was changed from a single button (Left/Left & Right) to two seperate button for each seat. Also, the roof racks were changed from the taller style to the style you see on all 2000-2003 models.

To answer your specific questions, neither HID nor a NAV system of any kind were offered until 2001.

The 2001 was the biggest change from the original introduction of the 1999 YM, adding things that weren't offered before. Not all things listed were standard. I will try to outline only the things that were new to the RX for 2001:

- water repellent front-door glass
- VSC (with badging on the front doors) - so TRAC (traction control) no longer offered or needed.
- Brake Assist
- new style steering wheel/airbag - wood/leather steering wheel and shifter optional
- chrome door handles, on vents, door sills
- full size spare is the same 5-spoke alloy as the other four, not a black full-size spare as before
- NAV offered
- HID's offered
- rear bumper protector
- compass for the auto-dimming mirror (non-nav versions)
- rear cup holder
- rear, center seat how has three-point seatbelt
- baby seat hooks for the back seats
- rear tonneau cover now has a handle, but essentialy the same
- heated seats now have high/low option
- trailer hitch design changed
- fuel tank size up from 17.x to 19.x (not sure of the specific sizes)

Of course, the 2004 RX is all-new. There is also the Coach edition model which was limited in production, and had slightly different packaging (also the first monochromatic RX other than the maroon colored RX of 1999 and 2000).