Ask your provider to give you a range of public IPs.
The option is to use destination based nat to utilise the single IP you will get and then forward traffic to each server depending on the port used. ie taffic on port 80 to your public IP will be forwarded to your web server, port 25 to your mail server etc.
How you do this will depend on your external router/firewall etc,
The best way, is to convince your provider to give you more IPs.