VPN

Depends on what your intentions are. The "most deployed" solutions include standard encryption (3DES or AES) and authentication (MD5 or SHA-1). If you have a firewall with VPN functionality for both site-to-site (gateway to gateway) or client-to-site (remote user to gateway) you may already be most of the way there. Nowadays, most firewalls do offer encryption. It may be cheaper to add that feature/license in there if you don't have it already. If you don't have a firewall (get one!) you can deploy VPN concentrators, which are devices that are dedicated to VPN access.

On the other hand, depending on your network load, you may find it worthwhile to get a concentrator if your firewall is already being overworked.

There is no "right" solution, but I have found that most small/medium businesses tend to use the firewall's site-to-site and client-to-site functionality. For larger networks (thousands of employees) a concentrator may be a wiser choice.

Hope that helps -