Pleas visit IDNRS.com type 'bookmarking' in domain search box, you will get plenty suggestions on next page
Ideas from dopedomains: BOOKLETTS.COM $5 (Buy) 2MARKIT.NET $10 (Bid) BOOKALIEN.COM $5 (Buy) and BOOKALIEN.NET $5 (Buy) BOOKANSEE.COM $5 (Buy) I found most of those by searching ^book and markit -Jason Dopedomains.com
I really think the domain name doesn't matter for a startup website. that is, because it would be very difficult to find an available domain names that will be related to your concept...you would have to pay a premium to get a decent domain...if you are welling to do so, then you have taken an additional step in your branding/name recognition. I'm a domainer, holding a large portfolio of domains. We "domainers" are GREDDY...believe me...we ask too much, cuz we are in control of the name that the buyer is interested in. other than that, you can start with any domain, the most important thing is marketing it and making it popular. look at google, what was google back in the 90s? nothing. today, the internet can go down without google. "i believe, because i believe in google"