If you are not in a hurry, check out Dell's Outlet
http://www.dell.com/outlet (not their DFS outlet). Many of the computers there are refurbs and they have 10-15% coupons coming out every month for Dell Outlet. Shipping is almost always free too.
I don't personally care for the Inspirons, but the Studio 540 and 540s (slim case) has Intel G45 chipset while the Inspirons have G3x chipsets. I only cared about this because the G45 has a much better IGP. The Vostro 220 series also has G45 chipset.
Watch out on the Studio and Vostro slims because their PSU is not a typical ATX PSU and I think it's only 250W which severely limits what you might be able to add on later. On the other hand, the smaller form factor can be nice to have depending on space. Also the slim machines only have low-profile expansion slots.
The Optiplex 760s are nice too, but they have Q43 chipset which doesn't have h.264 decoding like the G45; but they do have vPro and Intel AMT instead which isn't much use for a home machine. Since the Optiplexes are enterprise machines, where users will probably have network storage, their HDDs tend to be smaller compared to what you'll find on Vostros and Studios. The Optiplex is also BTX which is a bit weird, but the minitower only has one 120mm fan to serve as the case and CPU fan, but those things are very quiet.
The machines from Dell Outlet carry the same warranty and support as new machines. One year (can purchase more if desired) for Vostro and anything from Home section. Optiplex have three years standard.
I recently bought a Studio 540s with the following specs for $400:
Intel C2D E7500 (no VT)
Intel G45 chipset with IGP
4 GB RAM DDR2 800
500GB HDD
16x DVD-RW
Flash card reader
Includes wired keyboard and laser mouse, Win 7 Home