This deal has ended.
Just for today, Dell has their Vostro 200 Desktop for only $399 after $330 instant savings. This is well-configured enough for most people and relatively inexpensive if you want to upgrade (just scroll across the component icons at the middle). It comes standard with a 1.6GHz Intel Dual-Core processor, 1GB memory (upgrade to 2GB for $100), 160GB hard drive (upgrade to 250GB for $50), CD burner / DVD-ROM drive (this only reads DVDs; upgrade to a DVD+R for $30), Windows XP or Vista Home (I recommend XP, Vista isn't perfected yet), and a 19" flat-panel monitor (upgrade to 20" for $30). Shipping is free.