I will recommend is the REI (www.rei.com) Ex Officio Boxer Briefs for the followiing reasons:
They offer moisture-wicking and quick-drying performance to keep you comfortable - you can wash them nightly
Anti-bacterial finish hampers odors -
The sales person mentioned that all they military guys going overseas get a few pairs of these for the Anti-Bacterial thing.
Keep in mind they are expensive, but you only need 3 pair for a world trip.

Big enough for meat and 2 veg.

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TheBrightStuffDotCom

Why wear them at all except when its really cold? Just more clothes to wash.

Commando. Hands-down, the only way to go for me. Too damned hot on the road. The boys have to breathe. Then again, I'm riding an air-cooled Harley. I might feel differently on a liquid-cooled bike. I do wear underwear in the winter, though. When riding in the snowy months, I generally wear boxer-briefs and some North Face synthetic silk long underwear beneath my chaps.

I usually go commando anyway..... nice and breezy. ^^ But if I had to wear something, I'd wear the silk. You can get them at your local Wal-Mart for about $4.50 a pair. I know, kinda expensive compared to the packages of 3 pairs for about that price, but it's definitely worth it.

As long as it's brown...well, maybe black. Sorry.

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"There's no justice, just us".
2004 650 KLR, Central America

Silk:

Cool when hot, warm when cool.
Wicks sweat.
Dries qucik when washed, or when sweaty.
Doesn't chaff.
Comfortable fabric.
Natural fiber (more resistant to bactaria).
Packs light.

Tight boxers:
Prevents chaffing
Prevents wedgies

Synthetics:

Some people claim that synthetics are a breading ground for germs and bactaria which can lead to both smell and skinreaction.

Personally I will most likely go for tight silk boxers.

My suggestion:
Buy one of each (loose boxer, tight boxer, briefs, etc, in silk, cotton and synthetics) and test them out before your trip. A good way to test them would be by riding a bicycle as you would both be building up sweat and chaffing.

Hey! Great thread!!!

Unpadded cycling shorts usually get my vote.

My wife and I are getting ready for a RTW starting in July 2006 from China to Mexico. I had the same concerns and after quite a bit of research I found LDComfort in Washington state in the US. If nothing else, pls visit their site and learn the truth about underwear. They seem to be the only ones who have carefully looked at this problem. We now have three sets each,
Jack

Note that LDComfort sponsor this forum too - so click on their logo at the top of the page, and let them know where you heard about them!

Grant

LD Comfort
 

Based on this thread and the advert I decided to try a pair of the LD Comfort underwear. A bit pricey but if they last a long time then it'll be worth it. I remember buying underwear about half way through a year long trip and having some real trouble finding something that fit, was comfortable and quick drying. No success until we got back up into Europe.

I went for a short ride on the weekend to try the underwear out and they were indeed very comfortable. Another bonus was that I hand washed them and hung them to dry on the shower rod overnight and they were bone dry in the morning. So I'm thinking of just keeping the one pair for riding only and then giving them a quick wash at night. Then have two or three pairs of quick drying underpants for off-bike activities.

Pants
 

Sad when you need to talk about pants but here is my 2 pence worth.
Disposable pants are the way to go, the nursing mother type (from Boots in the UK). They are made of a material like dish cloth, and easily dry overnight.. yes they are washable & they are really comfortable. On our last six week trip we used 4 pairs each.
The only issue is don't go to the disco & hope to pull. The result could be catastrophic!!
LOONAL

Not worth goin cheap on yur undies, I like the exofficio boxer briefs and its woth it for them and some good socks. It amazes me how people are willing to pay $40 for a shirt then don't want to spend the $20 for underwear and $6-9 for socks when they are more important for your comfort. Chaffing and wet clammy feet are no fun.

Lycra polyester blend
 

The above blend, I find quite comfortable. They keep "things" in place and the material doesn't chafe. You can find them in most bike shops. I prefer the ones without the padding, however some like the padded ones. They dry quickly too.

well i'm back from my travels and I ended up going for Burtons cotton boxers - the snug fitting ones. Only had one seam up the back never gave me any problems. The only thing I would like to change on them is the fold-over seam round the base of the leg.

I ended up taking 8 pairs with me and changing everyday, made life easy as I just had to remember to call into a laundrette on the same day every week. By the end of the trip one or two pairs were getting a little saggy and lost a bit of support but they did me prowd.

Thanks for the many replies

Harvey