Some good suggestions here already!
Not knowing anything about you, or your age, or your likes and dislikes, i'll just recommend what I like

(not in any order)
1. Game of Thrones series - Books one through three are epic and get better and better as they go along. Then book four gets somewhat boring and book five is truly crap. But, the first 3 are sooooo good that its still worth reading the series.
2. Hunger Games series - light fun reading.
3. Thrawn Trilogy from Timothy Zahn - Star Wars books which are better than the Star Wars movies. Good for summer reading! (start with Heir to the Empire).
4. Ender's Game - Just a really fun sci-fi story about a kid put in a tough situation. Very good book with a mind blowing ending. Optional followup books are good too (at least the ones I've read so far)
5. Dune - Kind of heavy for summer reading but so brilliant and fun to read. When I take a break from reading this it takes me a minute to re-acclimate to the real world lol!
6. Harry Potter Series - Wonderful fun and easy reading. I enjoyed every single one of them. I could read 100 more Harry Potter Books. These books just make me happy.
7. Mistborn Series - Seriously good fantasy series which is quite different from the norm.
Some non-fiction in case that is your bag:
8. The Big Short - About the 2008 financial meltdown. Phenomenal book but only if you care to understand world events.
9. Into Thin Air - Agreed with SwingOnThis. Great read. Devastating story.
10. Steve Jobs Bio by Walter Issacson - Fun read but you probably know most of it being on this forum.
11. Einstein Bio by Walter Issacson - Better than the Jobs one. Very good read.
12. One of a Kind - Great story about a brilliant gambler.
I could go on and on but I'm stopping here. Have fun!