You really do NOT have a lot of variety for fonts on the web if you intend to be cross-OS compatible .. You are basically limited to really a handful of uninspiring choices.
If you want to get some "serious, formal, casual, inviting" fonts then you're going to need to create bitmap images in a graphics editor - which of course doesn't help too much if your content isn't static.
For dynamic content with an "unlimited" range of font treatments, what I would probably try is some PHP + GD or ImageMagick goodness to generate bitmaps on-the-fly.
