Small in size, but big in optional features - this is the 7400 series router.  This one-port adapter slot unit can take one of over 40 types of 7200/7500 series port adapters.  With it's 1U size and stackabiity, it's ideal for use in application specific routing deployments.

Models:

7401ASR-CP - 2x Gigabit Ethernet ports (RJ or GBIC), one expansion slot and 128MB of memory (expandable to 512MB)

7401ASR-BB - same as above, but with 256MB of base memory (also expandable to 512MB)