Well, F5's FirePass and Juniper's SA are SSL VPNs, so you just fire up a web browser, connect to whatever IP/URL the box is available on and then you have access to your company network. You can specify file share bookmarks, internal web servers, terminal servers and so on that you can connect to - all via a web interface. Or if you prefer, Juniper's SA has a feature available called Network Connect which downloads a client that provides full network access all tunnelled via SSL on port 443.
This is great if you mainly use web-based applications or for remote workers with laptops which have whatever software preinstalled. As an example, when I log into our SSL VPN box at work I'm presented with a list of web bookmarks, one of which is OWA or I can start up Network Connect then use my full Outlook client.
So it's different to Citrix in that you'd still need to have applications installed locally - with Citrix you can run the applications straight off the Citrix gateway whereas an SSL VPN just provides network access (or bookmarks for file shares/web links etc) tunnelled via port 443. Depends which way you'd like to go really, but I'm quite certain an SSL VPN solution is cheaper than a full blown Citrix AG setup.