I just want to test how frReader works, and I am looking for a reasonably good enough free ebook. Any recommendations? (I would like to keep it with my N770 for showing off to others when time comes)

did you try here?

the Baen free library has many free books.
http://www.baen.com/library/defaultTitles.htm

http://www.gutenberg.org has all the classics. gutenburg Australia has copies of some books that are still under copyright in the U.S.

http://fictionbook.ru/en

http://manybooks.net/

I wish eReader would support the internet tablet. Having pouring several hundred into eBooks I can read on my Cingular 8125 and my wife's Treo 650, I'd be in heaven if I could read them on my N800 or N810.

Last I emailed them, they wrote back "we have no intent to support the Nokia Internet Tablet as this time." I'm still trying to find a solution to reading contemporary fiction on my tablet. fbreader doesn't support Adobe activation and reading PDFs downloaded through Adobe eBookMall, does it? If it did, I'd be tempted to switch to a more tablet-friendly eBook vendor.

Trust me: Step away from Ereader NOW!

The reason? That reply they gave you (and me, and many others). Any DRM-based platform that doesn't come with an open source access program is to be avoided at all cost.

There are ways to recuperate your investment in Ereader material, ranging from a DRM-stripping program for Ereader books to simply torrenting the ebooks you already purchased in a more convenient format (Microsoft's lit format, although technically DRM-ed, is ridiculously easy to crack).

And if you need non-DRMed commercial books, these guys
http://www.ebookmall.com/
have lots of unencrypted ones. I'm sure there are other vendors that don't treat their customers as criminals...

A related question you did not ask is "What format is best for FBReader?". I started using Plucker, but have recently switched to MobiPocket which I still think is best for FBReader on a 800x480 screen. An alternative is .LIT exploded to .OEBZIP, which is good for "secure" e-books, and generally gives larger images than MobiPocket (which can be a disadvantage on the 770 if the images are too large for the screen).

Books I have used as examples include Ring of Fire:
http://www.webscription.net/p-352-ring-of-fire.aspx
from Baen's Free Library. This is good (e.g. as MobiPocket) because it is a collection of short stories navigable via its TOC and because there is an embedded image in the last short story. The very best examples are probably recent SciFi "magazines", such as Jim Baen's Universe or Grantville Gazette. These have extensive color illustrations which work very well in MobiPocket format on a 770. However, they are not free as e-books.

Another source of manually formatted public domain MobiPocket books is MobileRead at: http://www.mobileread.com/forums/forumdisplay.php?f=128

Heck, just use RTF or HTML. Even TXT is fine most of the time.