1. Dell Optiplex 390
If you have a business need there's a Dell Optiplex that can fill it. The Dell Optiplex 390 range is available in no less than three form-factors and starts at a highly affordable price, considering this comes from Dell with a year's on-site warranty and includes Windows 7 Pro either 32-bit or 64-bit is not to be sniffed at.
The base model ships with a low-end Sandy Bridge-based Intel Celeron G460 processor. It's actually quite capable at 1.8GHz with 1.5MB of cache, supports two threads, 64-bit instructions and includes on-board Intel HD Graphics 2000 with support for dual displays. Coupled with the standard 2GB dual-channel memory it may not set the world on fire performance wise, but that being-on-fire thing just distracts from editing office documents and replying to email.
Of course if you want more punch, Dell support ranges up to the Intel Core i5 quad-core processors and 8GB of memory, while warranty support can extend up to five-years.