Great idea.
A new Honorverse book by David Weber - great. Top of my list to buy in March.
As for keeping track of new releases, I use Fantastic Fiction -
http://www.fantasticfiction.co.uk. You can check on a favourite author or check for new or forthcoming titles. Even better you can limit it to ebooks by selecting Kindle. The only problem is the quantity - 933 Kindle books due to be released this month!
If you've got the time and the patience then its a good place to check. I found that Leslie Charteris' Saint novels have justed started appearing as ebooks. More to add to the wish list for puchasing.