Here are some ideas:
Time Warp Trio by Jon Scieszka
This is a great series (sneaking in history) that is really funny and simple.
My Weird School series by Dan Gutman
These are fairly simple, boy friendly, decently written books that my boys love.
Franny K. Stein by Jim Davis
Okay, I know the main character is a girl, but this is not a girly girl, and it's hysterical and very simple. Your kids will LOVE Franny.
Roscoe Riley by Katherine Applegate
Cute and sweet and fun. Great choice (way better than Junie, in my opinion).
And there's always Stink by Megan MacDonald
A little gross, but if you don't mind gross, it's pretty funny. Again, the writing is better than Junie B. too... (Can you tell I'm not a big Junie B. fan???)
And one more: George Brown, Class Clown by Nancy Krulik (Katie Kazoo author)
Fun. Not bad. Nice series. The first book is titled, Super Burp!
Next time I'll post books that a first or second grade boy would love to listen too—these are the type of books your child should be reading on their own, but don't read these out loud. Please. Read them something much better that will get their minds churning and will get them absolutely belly laughing with you. More on that next time...