It goes without saying that Michelle Bennett's post on Lots of Ways to Get a Singing Job Without an Agent is a definitive list of methods for a non-represented classical singer to achieve gainful employment through hard work, tireless marketing, right intentions, and a little luck.
I would add one more item to Michelle's list:
Employ a Publicist. More and more singers I know of that are getting work these days are doing so with the aid of a publicist that is not necessarily schooled in the ways of classical music, but in how to prepare a great package, issue press releases, arrange media coverage, and create buzz for their clients. As opposed to the old-school method of the agent contacting a closed group of presenters and arranging auditions, a publicist can create an image for an artist, find their niche, and determine which media are best for spreading interest.
Case in point: A recent posting on this blog came about after I had been contacted by a publicist (to be more specific, a boutique marketing consultant) that had thoroughly researched her clients' niche and the media outlets that would be best positioned to create a buzz. I was flattered that she contacted me with links to all relevant content, including video embeds, and then I posted the content which was indeed congruent with my blog's mission.
The only quibble I would have with Michelle's list, and this comes with a little experience of North American agencies, is that she should have named the list "Lots of Ways to Get a Singing Job Even If You Already Have an Agent". Even if you pay an agency for representation, the ultimate responsibility for getting work lies with the artist. I know lots of singers on the rosters of major agencies and have no work.
Michelle also writes that she has not had any success getting engagements via her blog so far. I think this is a shortcoming of presenters rather than any limitation of the blogging platform (which tends to create sites with greater SEO than many traditional sites). There is a definite niche of blogging performers around these days, including Michelle, Hugh Sung, Patricia Mitchell, Tom Meglioranza, Jeremy Denk, Ann-Carolyn Bird, Joshua Nemith, and myself (if I may be so bold). The advantage of hiring performers with blogs is that in addition to hiring the talents of the performer, they also in effect engaging free advertising on their performer's blog.
However, many people that I mention classical music blogging to end up looking at me as though I were discussing a genre of science fiction. Perhaps we're behind the times in this field, where a musician scheduling rehearsals on a PDA will still get responses like "Oooooh, you're utilizing technology!"
For the record, I get performing and administrative work from this blog, although to date it is much harder to get students from it.