There's also still the free xsi mod tool. valve used to recommend it after hl2 came out.
Autodesk discontinued xsi but there are still some good ressources around.
This one got me starting a while back:
http://www.veoh.com/watch/v1281981…XSI+6+Mod+Tool+
It's actually pretty handy for source props + the *.smd export works well.