Firewall, Remote Access VPNs, Virtual Firewall, Botnet Filtering, Anti-X, DOS prevention, user-based access control, URL filtering, IP Routing, NAT and what not!! WHAT NOT!!
If Routers are not cool enough for you, here are the Cisco ASAs.. WoW!
So, Currently Cisco rolls out various flavors of ASAs with varying performance, scale to meet requirements for businesses of all sizes.
Google out "cisco asa" and visit the first link. There's an ocean to dive into after Routing/Switching for me now.