Expect to be doing an uncomplicated design over the next few months. It's been a few years. Looking at Xilinx products page I see Extended Spartan 3A and Spartan 6 as being current, (although I know Xilinx does very well keeping product lines alive and I'm sure other Spartan families are also still available). I'm wondering what considerations should affect my device choice - don't need any newer features, DSP etc, and package selection is not an issue. What does "Extended" in "Extended Spartan 3A" mean ?
If the design's uncomplicated, you might want to stick with a Spartan-3A or 3AN device. The "Extended" family includes the 3A which requires an external configuration memory, the 3AN which has its own internal configuration memory, and the 3ADSP which has ample DSP-style resources. A few things point me toward the "older" devices.
The 3A devices are available in smaller sizes than the 6 and should be cheaper
The 6 family is relatively new with resulting tool maturity issues; they'll be cleaned up over time
The 3A devices are expected to have a very long life making later availability a minor concern.
They're all good devices. The 3As do have a longer, more mature track record and are likely to be "friendly" devices to work with.
This is just my opinion as a fellow designer who also watches the chatter on the comp.arch.fpga newsgroup.