I have a Linksys WRT54g and have been running DD-WRT for a few months. I am very happy with it. It allows me to ssh to the router and also use ssh tunnels.
Next steps for me are to setup mrtg and snmp for monitor stats + setup a method to send a WOL Magic packet to workstations inside.
DD-WRT Home Page
From Web Administration->Status->Lan->DHCP Clients Table
wl assoclist - shows all wireless client macs.
cat /proc/net/arp - shows all active clients in your network with IP and mac
dumpleases - gives you all DHCP-Client leases.
cat /proc/net/ip_conntrack - shows all incoming and outgoing connections