Get a nikon, its a best brand. Consider checking our books for some real estate tips.

for your purpose make sure it is user friendly, i would recommend the canon rebel series. great image quality and easy to use.
a used one would be around 400, check out ebay like this one

Nikon D90 DSLR body (built in autofocus motor) or Nikon F5/F6 SLR body(35mm film based) with Nikkor 24mm PC-E (tilt-shift) lens.

Buy a good book on photography to understand about perspective control lenses and how to use them for architecture and interiors.

I would suggest Nikon D5000.It has a very concise, simple, and easy to use interface. Picture out of it are good quality even in low light. The 18-55mm kit lens is good enough for wide angle shots

You can consider buying
1)Nikon D3000 10.2MP Digital SLR Camera with 18-55mm f/3.5-5.6G AF-S DX VR Nikkor Zoom Lens
*10.2-megapixel DX-format imaging sensor for prints up to 20 x 30 inches
*Includes 3x 18-55mm Zoom-Nikkor VR Image Stabilization lens
*Nikon EXPEED image processing; in-camera image editing and Active D-Lighting
*3.0-inch color LCD screen; 170-degree wide-angle viewing
*Capture images to SD/SDHC memory cards (not included)

2)Panasonic Lumix DMC-FZ35 12.1MP Digital Camera with 18x POWER Optical Image Stabilized Zoom and 2.7 inch LCD
*12.1-megapixel resolution
*27mm wide-angle Leica DC Vario-Elmarit lens; 18x optical zoom with POWER O.I.S.
*HD movies with 1280 x 720-pixel resolution; AVCHD Lite format
*2.7-inch TFT LCD screen
*Capture images to SD/SDHC memory cards (not included)

3)Canon PowerShot SX20IS 12.1MP Digital Camera with 20x Wide Angle Optical Image Stabilized Zoom and 2.5-inch Articulating LCD
* High-powered 20x wide-angle optical zoom with Optical Image Stabilizer
* Capture 720p HD movies with stereo sound; HDMI output connector for easy playback on your HDTV
* 2.5-inch Vari-Angle System LCD; improved Smart AUTO intelligently selects from 22 predefined shooting situations
* DIGIC 4 Image Processor; 12.1-megapixel resolution for poster-size, photo-quality prints
* Powered by AA batteries (included); capture images to SD/SDHC memory cards (not included)

4)Canon Digital Rebel XSi 12.2 MP Digital SLR Camera with EF-S 18-55mm f/3.5-5.6 IS Lens (Black)
*12.2-megapixel CMOS sensor captures enough detail for poster-size, photo-quality prints
*Large 3.0-inch LCD display; includes Canon’s EF-S 18-55mm, f3.5-5.6 IS zoom lens
*DIGIC III image processor provides fast, accurate image processing; improved Autofocus and framing rate
*EOS Integrated Cleaning system, plus Dust Delete Data Detection in included software
*Stores images on SD/SDHC memory cards (not included)

5)Canon EOS Rebel T1i 15.1 MP CMOS Digital SLR Camera with 3-Inch LCD and EF-S 18-55mm f/3.5-5.6 IS Lens
*New 15.1-megapixel CMOS sensor with DIGIC 4 Image Processor
*Includes Canon EF-S 18-55mm f/3.5-5.6 IS lens
*Full HD video capture at 1920 x 1080 resolution; HDMI output
*3.0-inch Clear View LCD; Live View Function for stills (Quick, Live and Face Detection AF modes) and video
*Capture images and video to SD/SDHC memory cards (not included)

6)Olympus Evolt E520 10MP Digital SLR Camera with 14-42mm f/3.5-5.6 and 40-150mm f/4.0-5.6 ED Zuiko Lenses
*Box Contents – E-520 body, Li-ion battery BLM-1, Li-ion battery charger BCM-2, USB cable, Video cable, OLYMPUS Master 2 CD-ROM, Instruction manual
*Up to 3648×2736 resolution – RAW (12-bit), JPEG, and RAW+JPEG File Formats
*CompactFlash Type I/II, Microdrive, xD-Picture Card (Dual-Slot) Memory Card Slot
*3.5 frames per seconds sequential shooting speed, up to 8 frames in RAW mode
*Dimensions – Width 5.35 x Height 3.60 x Depth 2.68 (136×91.5×68mm) excluding protrusions

Any will do. They are all basically the same. The cheapest right now is a Sony. Around $400. The kit lens will go from wide to short tele, enough for interior shots and general purpose shooting.