Can you recommend a pair of headphones which will cancel out human voices?

I went through about 3 pairs of the cheap Sony ones linked to above before I bought Shure E3cs. I don't go anywhere without them. BART and MUNI, as well as airplanes, would be insufferable without IEMs. I still use Sennheiser HD280 Pros at work, but they're just easier to get on and off when I'm semi-mobile.

Just thought I'd update this thread for future readers - I ended up purchasing a pair of in-ear monitors and a pair of http://www.jabra.com/Sites/Jabra/AU-EN/products/Pages/JabraC820s.aspx. I find the in-ear monitors are good for the bus but too uncomfortable to wear for more than half hour or so (for me anyway). I use the Jabra's for work and, although human voices still get through, between the active noise cancelling technology and the beautiful sound quality it becomes very very easy to ignore them. When I'm wearing my Jabra's at work I can concentrate so much better and effectively ignore any external sound that comes through my headphones much easier because so much of it is already blocked out. The Jabra C820's are a knockoff of the Bose QuietComfort series of headphones, but at a fraction of the price (I picked mine up for $80 including shipping from http://www.hifiexpress.com.au/ in Australia) they're a very good deal. They're also super comfortable and I can happily wear them for 8+ hours straight. The sound quality is also excellent.

Thank you so much for all your responses, I really appreciate it :)!!

Another vote for the Shure in-ear models. If you can afford it, go for at least a step up from the basic models, as they're smaller and less likely to hurt. What really made them work for me was the triple-flange silicone sleeves - they've been very comfortable, and they come in packs with 3 pair. With a little fiddling, the seal is quite good, and I can pull them in and out all day without it hurting the canals. Also, I bought my headphones from Amazon, and when I asked their customer service if I could return them if they didn't fit, I was told that it wouldn't be a problem, even though I'd stuck them into my ears. Grain of salt and all that, but it was enough assurance for me.

In-ear, definitely.. I use Sure E4c's and they are a godsend. The foam attachments are the best.. the only downside is if you have to constantly take them in and out. Also, they isolate so well you won't hear the phone, or anything else.

For what it's worth, I have a $300 pair of Ultimate Ears (much like the Etymotics) and a $50 pair of Sennheiser in-ears.. and I tend to just use the Sennheiser. If the UEs are a 8 sound wise, the Sennheisers are a 7.. and they're smaller and easier to put in.

I have the Shure E4c's - and I researched them and Ety's as well as a few others in the passive and non-passive noise canceling market pretty extensively before buying. I was able to find them for about $200 online, and they're the best investment I've made in the last few years, hands down. Use the foam attachments for comfort, and you won't hear anything but what you're streaming in through the cord.

I think on a past question someone linked to DIY in-ear phones, created by making a mold of each ear, drilling a sound hole through and attaching some sort of driver. Don't have the link but it was awfully cool and probably would eliminate some of the pain associated with standard in-ear types for longer wearing.

I had Shure E3cs, and they work really well at blocking sound. I wouldn't wear them in the office though; they muffle footsteps and polite coughs enough so that people would have a hard time getting your attention, other than physically tapping your shoulder or waving something in front of your face. This gets annoying for both sides. Also, they're not really fun to remove and reinsert. Remember that they go inside of your ear canals, and form an airtight seal. Yanking them out of your ears really hurts. Doing it several times a day might get painful on the eardrums. You might want to consider earphones that have a worse seal (and block less sound) like the above-mentioned Sony Fontopias or Creative Lab EP-360s.