The $99 Wonderboom is the latest wireless speaker from Ultimate Ears. It sounds great, and even floats -- making it the perfect speaker if Dad spends his summer around the pool.
The Wonderboom's predecessor, the UE Roll 2, is also fully water-resistant -- and can be found for as low as $55.
If Dad prefers a more "totally tubular" waterproof wireless speaker, the $99 JBL Flip 4 is a great choice.
The Flip 4's predecessor, the Flip 3, is still pretty great, and you can find it on sale for closer to $80.
Moving from speakers to headphones: The 1990s-era Sony MDR-7506 may well be the best-sounding headphones you can get for under $100. Just like Dad, it's an oldie but a goodie.
With its stainless steel build, the $99 Beats EP may be the best value in the Beats line. It comes in black, white, red and blue -- but it's for cool dads only.
Maybe you don't want to spring for a new Apple MacBook or MacBook Pro for pops, but if he's got one already (or another USB-C based notebook that's got limited port options), Kingston's Nucleum ($80), the ultimate USB-C hub, is a good accessory for it. It allows you to add external ports for HDMI, USB-A (2), micro and standard SD memory cards, as well as an extra USB-C port.
This in-ear headphone is an older model, but it delivers solid sound -- and it's a lot more of an affordable Bose-branded gift for Dad than a Wave Radio.
If Dad is more about sound quality than familiar brands, consider the 1More Triple Driver. It's one of the best sounding in-ear headphones under $100.
If Dad's ready for wireless headphones, there are plenty of great choices in this under-$100 range. The Plantronics BackBeat 500 is one of our recent favorites, considering its $80 price tag.
The older BackBeat Sense wireless headphones have also dipped just south of the $100 mark.
If Dad is cool enough to rock the skull logo, these $65 Skullcandy Grind Wireless headphones are a good choice.
Is Dad a runner? The sporty BackBeat Fit wireless headphones may be just the ticket.
Monster's Adidas-branded Sport Adistar In-Ear Wireless ($100) is one of the better fitting in-ear wireless sports headphones -- and it also sounds decent for the money. Another good choice for dads who run.
If your budget for Dad is limited to around $60, the Sony MDR-XB50BS wireless in-ear headphones are a worthy choice.
Jabra Halo Smart is a wireless "neckband" model. Its stereo earbuds magnetically hold together around the neck when not in use.
You can't get Dad an iPad for under $100. But the next best thing is the Amazon Fire HD 8. At just $90, it's a steal.
Amazingly, Amazon's Kindle Paperwhite e-reader is actually more expensive than the Fire tablet. But this $119 unit is often discounted to $99. It's a good choice if Dad is a bookworm who enjoys distraction-free reading.
Turning to video streaming: There are plenty of Roku models at $50 or less. But in the $100 range you'll find the Roku Premiere+. It's worth the extra cash if Dad has a 4K TV with high dynamic range (HDR) video compatibility. But even if he doesn't, he'll like the Wi-Fi remote (no pointing needed) with a headphone jack for private listening.
The best alternative to Roku at this price point is the Amazon Fire TV. The core Fire TV bundle is now $90, the antenna bundle is $100 and the gaming edition bundle (with gamepad) is down to $130.
If Dad prefers controlling his video from a phone or tablet -- and doesn't need to watch Amazon Prime video --check out the Chromecast Ultra, which also has 4K and HDR compatibility.
If Dad still has a big collection of discs, go for the Samsung BD-J5900. It will play all of his DVDs and Blu-rays, but has access to the major streaming services like Netflix and Amazon, too.
If Dad spends all day on his Mac or Windows PC, he'll appreciate a top-notch mouse like the Logitech MX Master.
If Dad still spends a lot of time on the road, opt for the MX Anywhere 2 mouse instead.
Another good gift for outdoorsy dads: Biolite's $80 SolarPanel 5+ is equipped with an internal battery that stores energy from the sun, which means he can keep a charge in reserve your for phone and other devices, although tablets will take longer to charge.
Another good gift for road warrior dads: The Mophie PowerStation Plus, an external battery charger starting at $60, has an integrated Lightning cable with a micro USB adapter so he can charge a variety of devices.
With two dimmable bulbs and a control bridge included, the Philips Hue White LED Starter Kit is possibly the easiest way to get Dad onto the smart home train.
The NES Classic would've been the perfect retro gaming gift for Dad -- except for the fact that Nintendo just discontinued it. But don't pay big bucks on eBay -- get him a Nintendo 2DS instead. At just $80, it's the most affordable way for him to relive his childhood with games from the Zelda, Metroid and Mario series that he can't get on his phone. Even better: Mario Kart is thrown in for free.
Does Dad have a recent Samsung Galaxy phone? The latest Gear VR headset will turn it into a full-fledged virtual reality headset, with a cool new controller to boot.
The same goes for owners of Google's new phones. The $79 Daydream View turns the Pixel and Pixel XL into VR viewers -- and it includes a small controller as well.
Dad can channel his inner Han Solo with this Millennium Falcon drone. And Mom will appreciate its crash-friendly foam body. Priced around $80.
If $100 is outside your budget, don't worry: We have a whole separate list of great Father's Day gift ideas for under $50, too. Spoiler alert: The Amazon Echo Dot shown here is at the head of the pack.