arp -a is fast and easy, but I have found that under certain circumstances, it doesn't list all of the devices. (As an aside, I don't know why that happens. Any ideas?) Here's an approach that -- so far -- always appears to work. It just takes longer...
In a shell window on your host machine (you said you did want to log in using ssh, right?), type:
sudo nmap -sS 192.168.1.0/24
(This assumes your local network is 192.168.1.xxx). This will scan for devices on the local network. It may take a while, but when it completes, it will print out a number of entries, including one that reads something like this:
Nmap scan report for raspberrypi.home (192.168.1.8)
Host is up (0.016s latency).
Not shown: 997 closed ports
PORT STATE SERVICE
22/tcp open ssh
5900/tcp open vnc
6000/tcp open X11
MAC Address: 80:1F:02:DA:AF:0D (Edimax Technology Co.)
From this, we know the DHCP-assigned address is
192.168.1.8. If you're using the default user account, it's now possible to log in via:
$ ssh firstname.lastname@example.org