Here's some of the XML databases we're looking at here, in no particular order:
Exist
Current front-runner. Cheap (free), implements XPath, with nice ties into XML-RPC and JSP. Implements the XML:DB interface too. Seems fast, but wondering how it will scale up, or react in a "real" environment (outside of the test apps that ship with it). Rob is investigating this now, and has a copy of our entire metadata repository stored in it as native XML files. It has a cool file structure metaphor, so it's like SSH'ing into a box to browse files and run queries.
NOTE: I had originally incorrectly stated that Exist implements XQuery. I meant XPath. XQuery is listed as a possible future feature for Exist, but it is not currently supported.
Xindice
Was the early frontrunner, but was too dog-slow to use.
Tamino
Was the original second choice, but is waaay to expensive, and only runs (well) on Windows servers. We need to be able to deploy on anything, especially MacOSX and Linux. Has amazing technology, though. VERY fast, dynamically indexed, etc... Very impressive stuff, but it's too bad their sales reps were so darned arrogant. "MacOSX? NOBODY is using that! If you want an easy install, just install linux on an old P3. That would work better." Thanks...
Sybase
Looked at WWDC2002, but XML support wasn't cooked yet. Am looking at it again. Hybrid SQL/XML database (but sounds like they are stored as separate beasts).
Oracle.
Too freakin' expensive for us.
Openlink Virtuoso
Haven't looked at it yet, but sounds cool. Hybrid SQL/XML database, and it sounds like you can run SQL-ish things on XML, and XQuery-ish things on SQL... Odd?