According to Cisco, the Cisco 7200 Series Routers are:
Application versatility supports managed network
services, WAN and broadband aggregation, MPLS, VPN,
QoS, and multiservice environments
Business-class security includes stateful
inspection firewall, software and hardware VPN
encryption, service-level validation features, and
intrusion detection
Multiservice data/voice features include analog
and digital voice, Survivable Remote Site Telephony,
and multiservice interchange (MIX)-enabled backplane
According to Cisco, the Cisco 3800 Series ISR Routers
are:
Designed for medium-sized to large businesses
and enterprise branch offices
Wire-speed performance with services enabled at
up to T3/E3 rates; increased services density for
security, voice, caching, video, network analysis,
and L2
Security features include hardware-based VPN
acceleration, antivirus defense through Network
Admission Control, IPS, and SDM support
According to Cisco, the Cisco 2800 Series ISR Routers
are:
Designed for small to medium-sized businesses
and enterprise branch offices
Wire-speed performance up to multiple T1/E1/
xDSL rates, increased services density for security,
voice, caching, video, network analysis, and L2; and
switching
Security features include hardware-based VPN
acceleration antivirus defense, IPS, and SDM support
According to Cisco, the Cisco 1800 Series ISR Routers
are:
Designed for small to medium-sized businesses
and small enterprise branch offices
Available in both fixed and modular
configurations
Wire-speed performance with secure data services
enabled at up to T1,E1, or xDSL rates
Business-class security with stateful firewall
with URL filtering, VPN 3DES encryption and Advanced
Encryption Standard (AES), Dynamic Multipoint VPN,
IPS, and secure wireless LAN option
Secure WLAN option for simultaneous 802.11a and
802.11b/g operation with use of multiple antennas
deployments 
