I'd like to know if there are any places online to download or order BVH (motion capture) files? I'm getting into animation a lot, and I'd like to try to find some pre-made motion captures as I don't have any such equipment to make these things myself (with the exception of Poser)

Try Credo Interactive. It sells mo-cap bundles specifically for Poser (both human figures and animals), at very reasonable prices.

DAZ 3D has or brokers a few bundles, also.

wolf359, cmdctrlesc, davidm, and pdblake all have some stuff here in the Marketplace.

If you have money to burn, try Turbo Squid. A single file can easily go for $25 or more there.

You can download free BVH files off the Internet, but they'll often need work after importing into Poser.
Link #1 (30MB download, lots of files)
Link #2 (a few dozen more)

I've a few freebies here for download but there is an extremely good program that enables you to make your own animations, it's called Poser...

BVH files are a great short cut but most of the free ones
are not exactly poser ready and will have to be corrected in the graph editor so be prepared to learn the poser graph editor to get
the most out of your BVH files.

Good luck!

Definitely expect to do some tweaking once you get them back in Poser. I downloaded some of the free ones and when I applied them to Vicky, she started walking around like Marlene Deitrich.