They have Mobipocket, MSReader, something along the lines of "Rocket" which I can't recall, PDF, and HTML. At least 3 of the 5 can be easily converted, or since you're in the US, you can just get the B&N version, which happens to be ePub (when downloaded using Windows or via NookStudy) and DRM-free (yes, I checked).
Might as well mention more assorted Romance, Thriller, and Christian ePub freebies of various DRM status which may have gotten lost amidst all the posts since they were put in as updates to Kindle-labeled threads:
Mr. Darcy's Diary, Austen-based romance by Amanda Grange.
Sony,
B&N,
ADE-ePub direct from publisher, which bills its Landmark imprint as 'the leading publisher of Jane Austen-related fiction", for which this author has apparently also written
Mr. Darcy, Vampyre. This may or may not influence your decision to download.
To Conquer a Highlander, historical romance by Mary Wine.
B&N
Outlander with Bonus Content, historical time-travel romance by Diana Gabaldon, 1st in a very long series.
Sony, Kobo US-only (sorry, can't dig up the link myself due to Kobo's IP geolocation),
B&N. Also @ Borders.
Sandman Slim with Bonus Content, urban fantasy thriller by Richard Kadrey.
Sony.
B&N.
Kobo.
The 7th Victim, FBI thriller by Alan Jacobson, 1st in a series.
Kobo,
B&N. Also @ Borders.
Rain Song, Christian contemporary romance by Alice Wisler.
B&N.
Dawn's Prelude, Christian historical romance, 1st in Song of Alaska series by Tracie Peterson.
B&N.
Intervention, Christian thriller by Terri Blackstock, whom I've occasionally seen described as one of the more "secular" Christian Fiction writers.
Sony,
B&N,
Kobo. Also @ Borders.
The DNA of Relationships, Christian self-help by Gary Smalley.
Sony,
B&N.
The Power of a Whisper: Hearing God, Having the Guts to Respond, Christian self-help by Bill Hybels.
Sony,
B&N,
Kobo.
Ian Rutledge: Mysterious Profile #24, behind-the-scenes promo packet and excerpt chapters from mystery series by Charles Todd, a pseudonym for a mother/son writing team.
Kobo,
Sony,
B&N.
The Story of Crass, punk music history/biography by George Berger.
Kobo. Also @ Borders.
My Baby Rides the Short Bus, inspirational anthology for parents of special needs kids.
Kobo. Also @ Borders.
I think that's everything reasonably recent that hasn't expired and isn't basically a permafreebie like those Harlequin and Star Wars and Naughty Nooners books.
For more B&N freebies, as always, their poorly updated but occasionally useful
Free eBooks page which still has a few time-limited ones not listed above, along with a bunch of glorified previews and Smashwords stuff.
Sony, sadly, has no such likewise page. At least, not one that's of any real use.