The beginning of the month is the best time of the month, because that's when most of the free and discounted ebook promotions start. There haven't been very many yet — I think because of the holiday weekend — but here are a few to get you started:
Wish, a YA novel from Scholastic, is currently $2.81. This is usually $9.99 for the ebook, though. I don't know how long it has been on sale, or whether it'll remain on sale for the entire month, but I recommend getting it ASAP if you are interested!
The Blue Light Project is actually Barnes & Noble's Free Friday selection for Friday, July 1st. B&N doesn't seem to make links available for free ebooks, so the image of the book's cover links to the product list. Just scroll down until you find the ebook listing to get the free ebook. Don't wait, though — there's no telling how long a Free Friday selection will be free! Sometimes they are free for a month, sometimes they don't even last the entire week before they return to normal price.
The Black Echo is B&N's Spotlight selection for July. Every month they offer an ebook for just 99 cents, usually the first of a series, so obviously the intent is to promote the author's other books. This one should be available all month, but be aware that they typically return the ebook to its original price before the last business day of the month officially ends. When I was browsing the June promotions on Thursday, around 6pm, I was finding that most of them had already returned to original price.
Shadowmagic is a children's book (ages 9-12) from HarperCollins that is currently priced at 99 cents. HarperCollins is doing a lot of sale-priced ebooks this summer, many of them YA and children's — I downloaded several last month as well. I'm not a big fan of HarperCollins right now, thanks to their library lending stunt earlier this year, but I guess I don't mind buying an ebook from them that is so steeply on sale they probably aren't making any profits on it!
I don't know if this vegetarian cookbook is usually free or not, but I suspect it is only free as a holiday weekend promotion. Again, there's apparently no affiliate link for free ebooks, so you'll have to click on the cover, and then scroll down to find the listing for the ebook.
Have a great 4th of July weekend!