Sure, you can put them elsewhere, but then you need to copy the tld files out and into your WEB-INF directory. I think I'd rather just have the full JARs myself.
Hm, I thought I tried that. Probably I forgot to put a proper taglib element in web.xml... Anyway, it worked this time with the jar files in jboss3.2.6/server/default/lib
I like this setup - if you have a lot of web applications deployed it's a good saving on JVM memory - a jar gets loaded only once.
Unless you are using scoped deployments, the JAR file would only get loaded once anyways.