I'll say it again:
Please let us know the budget. You tend to get what you pay for with headphones and some of them are VERY expensive. It really doesn't make much sense to make any recommendations without at least knowing your budget.
Ideally we also need to know what your husband will use these headphones for and where he will use them. Many of the headphones already suggested in this thread are exellent for SOME applications but can be very poor for others.
Simply asking about "headphones" is a bit like asking someone to go to the store and buy a pound of vegetables, when you really need tomatoes. Of course, you MIGHT get tomatoes... but you might also end up with a brussel sprout pizza.
Will he only use the headphones for practising bass? Most decent headphones will be ok for this. For practising I tend to prefer closed back headphones that also sit firmly on my head, as they give me better isolation from any distracting noise and won't fall off my head when I'm playing. I don't need neutral sounding headphones for practising, a bit of bass boost can be fun. I also don't use my most expensive headphones for this. Practise headphones are expendable items in my world.
For recording? I would use more or less the same type of headphones as for practising, although maybe ideally more neutral/detailed sounding to get a better idea of the actual tone of the instrument. At least if this for serious recording.
For mixing? I would strongly recommend open back headphones as most of these models tend to have a better soundstage and a more neutral sound than most closed back headphones. I also avoid headphones that sit very tightly on my head for mixing sessions as it can get a bit uncomfortable. Weight may also be an issue, some hi-end headphones can be rather heavy. Mixing will always be a compomise with headphones though, and you'll need rather expensive headphones (+ a good headphone amp) for the best results.
For casual listeing? What kind of music? Some headphones can be lots of fun with many "modern" genres of music but sound horrble and fatiguing with classical music or jazz. Other headphones can have amazing detail and soundstage with classical music but lack the punch most people want then listening to other types of music.
Does "leakage" of sound into the room matter? Have you ever been annoyed when you can hear lots of leakage from someone playing loud music through their headphones on public transport? Would this be a problem? Then you should avoid open back headphones, as they WILL leak sound. Open back headphones are also poor for recording vocals or acoustic instruments as the leakage of the backing track (or click track) will be picked up by the mic.
Is portability important, or will he only use the headphones at home?
It also matters what he will plug the headphones into. Impedance is the key word and this is IMPORTANT. As a general rule:
-Lower impedance headphones (8-32 ohms) work best with portable devices but aren't ideal for use with studio gear.
-Medium impedance headphones (around 32-100 ohms) are "allround" headphones that will be ok in most situations but may struggle a bit with portable devices and not be the BEST choice for professional studio gear or hi-end headphone amps.
-High impedance headphones (anything above 100 ohms but typically 250 ohms or higher) have the best sound but need a VERY good headphone amplifier to drive them properly. They will sound weak/thin and lacking in volume with most consumer grade equipment and be more or less useless with portable devices.
To make matters even more confusing, some very popular models of headphones are even available with different impedance ratings, depending on what you need the headphones for.
This may all sound a bit nerdy but it matters. A LOT. Especially the part about impedance. Some headphones are designed specifically for expensive studio gear or high end headphone amplifiers but will perform very poorly with lower grade equipment. Other headphones are (more or less successful) attempts at "allround" designs. And some are designed specifically for portable devices but won't sound great for other applications.
Medium impedance headphones are usually the safest choice for allround use, but not necessarily the best choice for every situation.
If I HAD to recommend one specific model without knowing any further details it would probably be the Beyerdynamic DT-770 Pro (80 ohms). This is assuming he will use them mainly for practising bass and maybe a bit of recording but doesn't own any high-end studio gear or a high-end headphone amplifier. These headphones will also be very nice for casual listening with most genres of music. They should also work ok (but maybe not ideal) with portable devices. They're not a good choice for mixing though (but few headphones are, and most of them are far more expensive).
