The cost involved with sending novel submissions through the postal service has always been a burden on most writers who don't have agents, especially those who live outside the U.S. Now that finances are tight for everyone, it's really important to cut back on expenses, and that may mean some writers choose to submit to fewer publishers or on a less-frequent basis.
Although it's difficult to find novel publishers who will accept electronic submissions from unagented writers, it's not impossible. I did some hunting around and put together this list in about thirty minutes:
Absolute Xpress has an online form you fill out and submit for your query to them (novella and novel-length science fiction, fantasy, horror, dark/gruesome fantasy, romance, erotica and mystery.)
Baen Publishing accepts full manuscript + synopsis novel submissions, and "strongly prefers" they be submitted electronically -- for specifics, check out their guidelines here (SF/F, military fic)
Black Death Books is reopened to novel subs as of Jan 1st and no longer accepts hardcopy submissions (way to go green, guys); they'd like to see a brief synopsis and first chapter, more details in their guidelines here (horror)
Newly-opened e-book/print publisher Eternal Press wants to see short stories as well as novel subs (synopsis and first three chapters on book-length fiction) via e-mail only (all genres but no YA)
eTreasures Publishing is presently looking for novel-length erotica only (guidelines available via e-mail.)
Juno Books prefers to see three chapters and a synopsis (due to tight schedule they recommend you have a finished manuscript before you sub) via e-mail (fantasy novels with a strong female protagonist)
Kensington Publishing does accept queries via e-mail: "You may QUERY ONLY by e-mail. Do not attach manuscripts or proposals to e-mail queries. An editor will respond if he or she is interested in seeing your material based on your query." (See guidelines for which editor handles what type of fiction; they publish pretty much everything.)
Nocturne Books accepts electronic subs of novellas (unpubbed writers are required to submit complete manuscript) for the new Nocturne Bites e-book program.
Also from the folks at Harlequin, Spice books is looking for novella-length erotica for their Spice Briefs e-book program; as with Nocturne Bites they want to see full manuscripts from unpubbed writers.
Twilight Times Books will be open for book-length submissions from Feb 15th through Mar 5th this year and accepts "cover letter, synopsis, first chapter and marketing plan" via e-mail (currently accepting nonfiction only, but they're interested in seeing the following categories of nonfiction: "Creative nonfiction, fantasy, historical, how-to books, humor/satire, juvenile, literary, magic realism, mainstream/contemporary, military/war-related, mystery/suspense, nostalgia-related fiction and non-fiction, paranormal, regional, science fiction, specialty/New Age, supernatural, the Sixties-related (fiction or nonfiction), World War II-related, women's fiction, writing advice, etc.")
Note: I'm not suggesting that it's better to submit to a novel publisher who accepts e-subs over mailed hard copies; you should submit first to the publisher for whom you think your work will likely have the most appeal. But there is nothing wrong with sending some queries or partials to publishers who accept e-subs, either. It won't cost you anything except the time to prepare the e-mail, and you'll be putting your work in front of another editor who may like it more than the dude in NY with the nine-foot-tall slush pile of hard copy manuscripts that he may or may not read sometime during the next year.
For more publishers who accept e-subs, check out the Book Publishers listings over at Ralan.com (also where I found about half of my list.)