What ports do I need to open in my firewall? [DirectAdmin]

20,21: FTP. Note that ftp will use a "random high port number" if the client is in PORT mode, so you may need to add a port range into your /etc/proftpd.conf file to allow ftp connections, eg:
 

and then open that port range as well in your firewall.

22: ssh access

25: smtp for exim to recieve email

53: dns (named), so your sites resolve

80, 443: apache traffic, http and https

110: client pop email access
143: clients imap email access

2222: DirectAdmin Access

3306: mysql acess. You don't need to open this port if you don't want to allow remote mysql access, as most mysql scripts are all accessed locally.