I'd suggest writing an add-on or utility for a popular data-managing server. You'll learn a lot and perhaps create something many others can use without having to get in too deep.
Here are some suggestions. I personally like the databases listed but I put the cache stuff first since thats what you seem to like.
Here are some suggestions. I personally like the databases listed but I put the cache stuff first since thats what you seem to like.
Cache / Proxy tools: http://www.squid-cache.org/ http://haproxy.1wt.eu/
Web Servers: http://www.apache.org/ http://www.lighttpd.net/ http://nginx.net/ http://www.acme.com/software/thttpd/
Databases: http://www.postgresql.org/ http://www.sqlite.org/
Version Control Systems: http://subversion.tigris.org/ http://www.selenic.com/mercurial/wiki/ http://darcs.net/ http://git.or.cz/