However, uninterruptible power supplies are usually a better investment than power-loss resilient storage media. The problem is, even if your SSD or hard drive behaves perfectly during a power-loss scenario, your server software may not. Almost every database, filesystem, etc. includes some amount of buffering in memory, because sending every write directly to disk is a performance killer.
Also, the best-case scenario with power-loss resilient media is that your system shuts down cleanly. With a UPS, you can keep the system up until diesel generators kick in, a much better endgame for everybody.
I once asked someone who had worked in the hard drive business what a hard drive would do when power was lost. "Try to park the drive head immediately before it crashes on to the platter," was the immediate response. Trying to flush the cache contents wasn't even remotely on his mind. In practice, losing power while writing to a hard disk does often corrupt sectors-- even sectors that weren't being written to during the power loss incident.
It's good to see that (some) SSDs are at least trying to flush the cache, but you really have to ask yourself: can you really trust the manufacturer's claims? And if you can trust them, can you trust your specific software configuration under this unusual scenario? I think it's just too long a frontier to guard with too few sheriffs. Dude, you're getting a UPS.