For that price, I would grab a 1DMkII. That sounds like a pretty good bargain. Its about the same price as my 450D when I purchased it new (well, perhapse a couple hundred more), and even though the 450D has a larger MP count, the 1D still has several advantages:

• Larger sensor (1.3x crop vs. 1.6x crop), so wider FOV
  • It'll make better use of EF lenses, however it will not be compatible with any EF-S lens
• Better ISO capabilities
  • Overall ISO quality is likely not that much better
  • You have extended range (50 through 3200)
  • You can adjust ISO in 1/3rd stops vs. 1 stops
• Much finger grained control over most settings
  • White Balance/Tint
  • Far more custom functions than the 450D
  • Larger range of exposure compensation
• Better Auto Focus system
• Higher flash sync speed
• Higher burst rate for continuous high-speed action photography
  • 8.3fps vs. 3.5fps
  • Larger buffer allowing more continuous shots without slowing down
• Better battery life (due to built in battery grip)
• Fully environmentally sealed and more ruggedly built
• Support for multiple types of storage (CF, SDHC)
• Many more benefits

On the flip side, there are some detractors:

• Older technology, using Digic 2 and 8mp sensor
• Smaller view screen (2" vs. 3", lower res)
• Compatible with fewer lenses
  • Only supports EF lenses, but is also not a full-frame sensor
  • Does not support EF-S lenses that a 1.6x sensor like the 450D would
• Larger and heavier to lug around than a 450D
• More complex camera that requires more knowledge to fully take advantage of