I would say stay with the cisco models... {I have used both Cisco and the Sonicwall products among others... Go with cisco or Sonicwall}

If what they have is a DSL unit in "Bridge Mode", then a Cisco 2600 or 800 would probably do the trick as a router.

The 2600 may be overkill for now, but if you plan on upgrading or for a modular design that would allow changing of hardware features (example.. switch to a T1 wic, etc) then the 2600 would be a better choice.

Although the routers have basic firewalling, you may also want to look at the 501 PIX firewall for the firewall/VPN capability if you have a small office.. [5-100 users]...

The PIX may be a little more complicated to setup than the consumer off-the-shelf devices..... {be sure to get the right license for the number of users you have} but remember it runs the same OS/software as the "big boy" PIX 515 corporate devices.

If what the ISP has is actually a DSL box with "NONAT" or "Fully Routed" mode then all that is needed might be the firewall itself (PIX) since that means that the device provided by the ISP IS already a router, just providing you with a public subnet... The 501 can act as a VPN endpoint for the cisco vpn client, a VPN endpoint for site to site vpn links, a dhcp server for the local subnet. Sincei it is a "true firewall", it has both NAT and PAT capability.. {hint... most off-the-shelf "firewall"/"Router" devices only do PAT...}