If you haven't seen it yet, CHI is the new replacement for the nice-but-slow Cache::Cache modules. I uploaded a DBI driver for it to CPAN. If you're skeptical of the value, try benchmarking MySQL against memcached. It's pretty close for this kind of thing, and on a local connection MySQL wins by a fair amount. It's also a lot simpler than trying to get memcached or Cache::FastMmap going on some random shared hosting provider.
I have another driver for IPC::MMA mostly done, which is looking extremely fast. After that will be BerkeleyDB.