Clientless SSL VPN
As the name suggests, the clientless SSL VPN solution just uses the browser. Users connect to the ASA with their browsers and through that session have access to internal HTTP/FTP/CIFS (windows fileshares). With additional plugins you can provide access to Remote Desktop, SSH/Telnet, VNC and Citrix, too.
Some "thick Client" applications are also supported with Smart Tunnels. From Cisco.com: "Smart tunneling allows Microsoft Windows users access to TCP applications without the prerequisite of administrative rights and allows VPN administrators to grant only approved applications access to internal resources."
AnyConnect VPN Client
The AnyConnect VPN client provides a full tunnel experience like the IPSec VPN Client, but does it with SSL and DTLS. This means that getting it through NAT devices or other firewalls is pretty foolproof.
Clients can launch the AnyConnect client in a few ways:
*locally user admin-defined profiles
*connect to the ASA and have it launch automatically
*connect to the ASA, login to a Clientless session and then launch the AnyConnect client.
AnyConnect is also the only way to get a full client for Vista 64-bit PCs.
IPsec VPN Client
The IPSec VPN Client provides a full tunnel experience for the user over IPSec. It is launched on the user's PC.
Unless you enable NAT-T or IPSec over UDP/TCP, users might have a problem connecting to your ASA when traversing NAT or another firewall.
Here's a link to a data sheet on Cisco's SSL VPN solutions.
Here's a link to SSL VPN Config Examples for the ASA:
Matt
CCIE Security