What's Good/Cool/Interesting to do in Bruges and Ypres?

I've been to Bruges, but I don't think there was any one thing that you had to see or do. Eat bowls of mussels, maybe.
It's very pleasant though, fairly compact and easy to stroll around. I like cities like this where there isn't anything you absolutely have to see (Brussels would be another example of this).

Haven't been to Ypres but I would imagine the main tourist things would be to do with the WW1 battle there

here's what not to do in Bruges: be there on your birthday, by yourself and get bitten on the foot while you're asleep by a spider. you will end up having your foot swell up to the size of jordan's retarded potato cat and you won't be able to do more than hobble for a few days. sitting and staring at a fucking fountain for extended periods of time sux.

I'd suggest going to Beaumont Hamel--the site of a tragic Canadian defeat in WWI--there's some amazing history about the Royal Newfoundland regiment. Also, I think Vimy Ridge (another Canadian site) is nearby. It's quite amazing. I really enjoyed checking out these places--I am Canadian, so it might have been more striking for me, but it still was a pretty amazing glimpse into the past.

drink trappist brews directly from the source in the seven storye monestaries peppered along the coast...

I second the Groeninge Museum...some of those paintings are really disturbing, including one stand-out of a guy being filleted.

One of the churches (check the guidebooks for the name) has a nice Michelangelo statue of Mary.

Go up in the tower for a nice view...one of the breweries also has a nice view (seen on the brewery tour - I forgot the name, but it was one of the more popular brewery tours).

Sorry I'm not helpful with the names...but...there was a hostel/club where I saw a free show by a spy/surf rock band from Ghent. Seemed to be a happening place, populated with a lot of locals. (Not being a local and being Asian, though, I stuck out like a sore thumb. After the show, I was just kind of standing around, and some guy actually just walked up to me and asked me what I was doing there, in English, in a kind of "You *obviously* don't fit in here" way. That was rude. But beforehand, two girls chatted with me, but I'm pretty sure they wanted me to buy them drinks. So...I'm not really sure if I have a point here.)

And, drink lots of beer, buy lots of chocolate, eat lots of fries and waffles...Belgians make those four things better than anyone in the world, ya know.

Get some Njintje (a.k.a. Miffy) books in the original Flemish - they make good party favors.