The Watchguard Firebox has all of the above features. As a firewall it performs brilliantly. The VPN features are handy - it can be used in a variety of configurations:
- VPN server for PPTP client authenticating against Active Directory or firewall itself
- Watchguard MUVPN, which uses Safenet VPN client authenticating against domain, LDAP or other
- manual IPSec tunnels
- Watchguard DVCP IPSec tunnels (really easy to set up an administer)
It falls down on the spam blocking. This is just a list of known spammers as black holes. Then again, I wouldn't set up e-mail filtering based purely on known IPs. You would want some additional filtering performed at the gateway level.
What are your exact requirements? If you only need to support relatively few VPN clients and your internet connection is only around 2MB, you could probably opt for a lower spec firebox and use the money saved on MailMarshal or similar.
Be aware that the firebox requires an annual subscription for URL filtering, web blocking, spam filtering to work.