Raid-1 won't set the world on fire for either speed or redundancy, but it's perfectly suited to some tasks.
Raid-5 is slow to write to disk, as it has to calculate the checksums on the polarity stripe. It also suffers from the write-hole issue (there is a delay between the writing of the data to disk, and the writing of the checksum
see this page for a better explanation than I can give.).
If you want the best of both worlds go for raid-10 (we use raid-10 exclusively at work). Raid-10 can read nearly as fast as Raid-0 (very quick indeed), and can lose half the disks in the array before any data loss happens (under ideal conditions).
The down side is it's not cheap, like raid-1 you lose 50% of your storage and you'll also need at least 4 disks to start with. But it's much easier for onboard raid controllers to implement, so you find it in more onboard raid controllers.
As firestar_3x says drives are getting more affordable, so I'd go for Raid-10 over Raid-5 every time now.
[edit]crikey, a whole batch of helpful posts appeared as I was writing this, so sorry if I repeated anything![/edit]
akakjs