I'd like to do nice typography on the web-- that is, fonts other than the limited set of "web safe" fonts.
Reasonable choices (considering accessibility and SEO) seem to be Cufón or sIFR or maybe @font-face.
Which approach has some blessing from font foundries? Are some foundries more web-friendly? I know there are free font houses, but I don't know of a good free font catalog.
sIFR or Cufón have both been very useful. @font-face isn't widely accepted by browsers, so you probably won't be very successful with that.
If you're using sIFR or Cufón I recommend only using it minimally for headers and subheaders. Both have scripts that will do automatic inline replacement of certain html tags with the flash element (hence, better SEO and usability)
As for licensing, both methods require you to embed the font so if you've paid for a font you will have to make sure you've paid for embedding rights. Cufón requires that the embed clause allows non-flash applications to also embed it.
It's not an easy to answer question as to what fonts support it - it's a per-font decision by whomever owns the font.
Generally speaking, Font Linking (e.g. @font-face) will violate the EULA for the font you're using, because it is based on redistributing the font file. Ergo, you can't. Of course, there are fonts which allow this.
Hoefler & Frere-Jones mentions sIFR in their FAQ under point 20: http://www.typography.com/ask/faq.php. To summarize, they are fine with it, as long as you take all measures possible to prevent easy reuse of the Flash file. I have not seen this from other foundries. That said, Flash embedding should be known by now, and IFR/sIFR is about six years old, with no lawsuits that I know of.
I am unsure about Cufón, since its rather easy to reuse a Cufón font file in different settings. But please note that I do not wish to spread FUD about a 'competitor' to sIFR, so take this as you wish.
Font Squirrel lists some good quality free fonts. Also see the Open Font Library, here and here.
As for licensing, I agree with Mark Pilgrim that the foundries should realize that their business model is absurdly flawed. Like the rest of software, fonts want to be free (because they are a work of design and redistributing them is essentially free), except it still makes sense to develop proprietary software for private use by a few clients. The whole purpose of fonts is to be seen, i.e. redistributed.