A lot depends on the style of furniture you already have in the room where the home office is going to go. Is it eclectic, modern, classic, transitional, Crate & Barrel, Pottery Barn, Mission, etc.?

Lots of places have nice looking desks and office furniture--Pottery Barn, Crate & Barrel, West Elm, Ikea, Ballard Designs, JC Penny, Home Decorators Collection.

What's going to make it work in either your bedroom or family room is how well it blends in with the rest of the room. Can you post pictures to give us something to go on?

I'm against office furniture in the master bedroom. IMO, working in that room brings too much stress into the room.

If you're buying new furniture, you might look into getting a rolltop desk so you can close it up when you're done and still preserve the looks of the room. You might also get a non office armoire so you have pretty furniture, but the the ugly stuff is out of sight. Also, I think you can buy lateral files that look like decorative pieces. You might get one that looks like a hall table and keep flowers or other decorative items on top. Depending on your set up, I think it is entirely possible to bring the office to the family room without making it look like an office.

I recommend you Google up a lot of photos on "home office", and especially for multi-purpose rooms (guest room/office). Also look up similar themes in deco books in bookstores.

Usually what you will find is attention to style, scale, and to using "non-office" items integrated into the group.
The ideas above about rolltop desk or antique (repro) secretary, drop-lid types work well. Or maybe a narrow writing desk with trunks or baskets for storage. Above a desk might be some decorative shelves with family photos and collectibles. Attention to a furniture grouping--so, not a clunky desk off by itself against a wall, but perhaps the correct size of secretary piece, an adjacent reading chair, a basket of magazines or books. If you have any area that is a "nook" or set off, that works especially well, but if not you can experiment with creating a vignette of a few pieces that looks like it belongs on a given wall, in a corner, etc. When thinking of these arrangements, you will need to balance form with function-- a lot of non-office office arrangements and unusual storage ideas are cutesy but a pain to utilize. That's important because in a multi-purpose room, you will want to try to keep the area neat, otherwise it won't matter what you have arranged, so you want your stuff to h help encourage your organization. But if you can find a slew of photos as I mentioned, some of them will be in spaces similar to yours, will suggest furniture types and placement and get you thinking outside the box.

You would need to complement your existing furniture unless you're doing a big makeover. For example, if you have oak LR furniture, you wouldn't plop a white Techline desk in there. But, you don't have to have a clunky oak piece just to try to "match"; you can integrate other woods, wicker, metal, glass in the right styles. If your furniture has curved legs or some more delicate or ornate style you would use some similar things. Second-hand shops, antique malls and estate sales will sometimes yield pieces inexpensively enough to be painted or re-purposed. Most commercial "computer armoires" are notoriously ugly, so you're trying to find something that doesn't scream particle board/computer.

In some cases, your "office" might need to be split up--for example, you might have the table or desk for your laptop in one spot, but use cabinetry across the room for some storage. This idea can be useful if there's a wall or corner that can handle (in terms of look or even wall load-bearing) more extensive cabinetry and shelving but that is not the place you want to sit and work.

Thanks for all the ideas so far.

I think the biggest sticking point right now is the lateral file. I've seen plenty of bookcases that'd work well in a family room. And I'm thinking an actual desk is not necessary, if we were to upgrade to a laptop we could carry that around and sit almost anywhere. But we seem to have a lot of paperwork on file. We filter thru it a few times a year, but seem to still end up with about 3 drawers full of "keepers". Right now it's in some (cheap ugly) basic 2-drawer lateral file from the Office goods store, plus 2 or 3 more plastic file cases in a closet. In order to free up this room, we need some file space that'd blend into other rooms, without making our home look like office depot. Our style is probably eclectic/transitional, so something Pottery Barn-ish would work fine. But all I ever see for file cabinets are tiny single-pullout drawers. I was thinking a lateral file disguised as a storage bench or TV console might work in the MBR.

If you have a dining room, that's another option for your home office. With a laptop, you could work at the dining table. Then find a lateral file that looks like a sideboard or something else that could be in a dining room.

I recently had to give up my home office so my youngest son could have his own bedroom. I moved the computer to the basement family room, under the stairs, on a small desk. I bought a small 2 drawer file cabinet that fits in my bedroom closet. I sorted out and pared down paperwork, then stored what I really need to keep in the closet. It works well. Don't imagine I have a large closet, either! It's tiny. I have a Shoes Away on the back of the closet door for shoes, so the floor space is pretty clear in the closet. The Shoes Away is the best organizing tool I have ever used. I've had it for many years (10+) and it's held up great.

Here is a link that might be useful: shoes away organizer

Just wanted to update to all who gave helpful info. Spent a crazy Saturday last weekend going to ~7 different furniture stores in a 40 or 50 mile circle.

Found some good candidates. These two are sort what we were thinking. They have the file space we need but won't look out of place in a family room. (And if we ever move to a larger home, they could go back into an office)

From Martin Furniture, Kathy Ireland Home, Tribeca Loft Collection:

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If anyone's seen similar goods from another manufacturer, please let me know. Thanks!