Build your own computer - one recommendation

http://www.newegg.com/Product/ComboBundleDetails.aspx?ItemList=Combo.467678
Here's another package deal that includes what I think is one of the better Intel processor (includes HD video processor on board and full virtualization support) and a very impressive motherboard, memory, hard drive (a good one) and a Bluray+DVD+CD-ROM drive (reads and plays but does not burn disks I think).  All this adds up to $467.98 but we still need the case, power supply, Windows, Office, keyboard, mouse.

Case and power supply deal:
http://www.newegg.com/Product/ComboDealDetails.aspx?ItemList=Combo.492901 ($99, but $85 after rebate)

Wireless keyboard and mouse combo:
http://www.newegg.com/Product/Product.aspx?Item=N82E16823126192 ($60)

Microsoft Office 2010 Professional Plus
http://www.techhead.org/k12/featured-products/microsoft-office-2010-professional-plus.html ($70 academic discount for those who qualify, but see if you might also qualify for a work-at-home license http://www.microsoft.com/education/license/manage/workathomerights.aspx for even less)

Microsoft Windows 7 Professional Upgrade (64-bit)
http://www.techhead.org/k12/featured-products/windows-7-professional-upgrade.html ($80 academic upgrade)

Totals:

Newegg.com $647.91
Shipping + 11.70
Total $659.61
-$35 rebate
$624.61 total Newegg purchase
includes a free 6ft HDMI cable and 8GB USB flash drive

Academic discount for Windows 7 Pro (make sure it's the 64-bit version) and Office 2010 which includes Outlook total is $149.98 + $7.56 shipping = $157.54

Not bad for keeping it all under $800.

This system would be very expandable and could get extra memory, add a discrete video card in a couple years, add extra hard drives and a DVD burner if needed, a TV tuner for recording live TV or cable making it a DVR, etc.  Initially the computer could hook up with a DVI cable to most any monitor or TV.  The keyboard and mouse are wireless and can be used several feet away.  You can add a TV remote later pretty cheap for another $20-25.  This system can play many new games, and handle just about anything.