If you're okay with sf/fantasy and are looking for zero-cost reads, then the Baen Free Library is your new best friend. The other thing that Baen has a lot of besides MilSF is comedic adventures and they've put quite a few among the freebies.
So if you're looking for modern zany stuff with action and possibly bad puns, you can't go wrong trying the following for free (I have not read all personally, but will note if I liked it/the author's other works):
Aaron Allston,
Doc Sidhe. Keep meaning to read this, but never quite get around to it. But it's got favourable reviews and ratings from quite a few people who say it's a fun pulp-style action/adventure.
Lois McMaster Bujold,
The Warrior's Apprentice, and
The Mountains of Mourning. If Ender's Game is one of your favourites, then I think you should definitely at least try Bujold's Vorkosigan novels, if you haven't already. They are truly excellent and worthy of the awards they've won. Not as overtly funny as the others I've listed here, but there's humour mixed in between adventure and poignancy.
Rick Cook's Wiz Biz series. Computer programmers and magic mix together, neither will be the same again. And also, the obligatory fight between the forces of good and evil. One of my favourites and recommended.
Caveat downloader: While the
Webscription listing for this implies that you'll be getting the omnibus edition containing the first two books, it seems to only contain the first book and you'll have to go to the
old Baen Free Library site to pick up the second.
Rosemary Edghill,
The Warslayer. You need to download this, if only to read the bonus fanboy-style episode summaries for the fake TV show in the book. Hilarious. The rest of the book is a bit more serious and less comedic than the premise might make you think, but still a light, enjoyable read.
David Freer &
Eric Flint,
Pyramid Scheme. This is also on the to-be-read list for me. I rather liked Dave Freer's recent Dragon's Ring which was a light humorous adventure and going by both description and reviews, this one significantly ups both the humour and the adventure, so it seems like it might be right up your alley.
And if you happen to like that one, the same writing team has done
Rats, Bats & Vats and
The Rats, The Bats & The Ugly, which are apparently a send-up of MilSF experimental super-soldier/combat creature tropes.
Keith Laumer, The Lighter Side. I know absolutely nothing about this except that Laumer is one of the more "classic" sf writers and this involves "a motorcycle-riding rutabaga-like alien" and "a beleaguered Satan asking a college professor for help when extra-dimensional aliens invade Hell itself". What's not to love?
Since it's a mix of longer and shorter stories, if you find you don't like his style, then at least you're not out much time discovering that.
No doubt others will chime in and suggest more Baen titles they've also found enjoyable. Happy reading!