I have a Linksys WRT110 router & an ASUS SuperSpeedN RT-N12 router.
Will either of these — possibly with my putting on third-party firmware — support VPNs? By that, I mean, by creating the VPN, not just mapping ports, etc.
You can set up VPN between two routers if both of them have appropriate software support. Some business class routers do have integrated VPN servers (for example Netgear FVG 318 and Cisco ASA 5505).
As for consumer routers, they usually don't have direct support, but third party firmwares can be used to make is available. For example OpenWRT has support for OpenVPN. Here's an article about it.
I'm pretty much sure that other free firmwares have VPN support too. Here's an article about Tomato and OpenVPN. You could also use one router as VPN host and have clients connect to it.
I don't think there's support for Linksys WRT110 among third-party firmware projects.
I wish. VPNs are not unlike web servers because a VPN is a server-client thing. That is, there is at least one server and at least one client involved.
There aren't really any dedicated VPN servers in routers because the companies that need VPNs in the first place will need them en masse in large server farms and hence the small stuff is not of interest.
What you can do is grab computing time from Amazon's EC2 service to build a VPN on their cloud, or run VPN software on your computer. Not the answer you're looking for, unfortunately.