I like the flexible ones, e.g.:
http://www.amazon.com/Norpro-Cut-N-Slice-Flexible-Cutting-Boards/dp/B0000VLU62/ref=sr_1_2?ie=UTF8&qid=1355927268&sr=8-2&keywords=flexible+cutting+board

I have a couple of the Epicurean Natural cutting boards and I love them. Totally dishwasher safe, don't warp, nice looking, easy on your knives, etc... http://www.bedbathandbeyond.com/product.asp?sku=14043810&utm_source=google&utm_medium=cpc&gclid=CNTEutTWprQCFa59OgodGnkApA

I'm surprised how well our plastic ones from Ikea have held up. I think I got two sets, so two small and two regular ones, and I use them every day and they work just fine, for a few bucks.

I love this: http://www.amazon.com/Architec-Gripper-Cutting-Board-14-Inch/dp/B0000AQXSP/ref=sr_1_2?s=home-garden&ie=UTF8&qid=1355930619&sr=1-2&keywords=cutting+board+gripper

I agree with @Ohwoah about the IKEA ones. I have put them in the dishwasher, although it doesn't specifically say you can, and haven't had any issues. But then again I don't use the heat-dry function when I do.

I like this one. It is made in the US, and BPA free. THere are also a few bamboo options out there like this one.

I second the Epicurean cutting boards. Not plastic but dishwasher safe and easy on knives. We've had several for years that go in the dishwasher just about every day and have held up great. We've even given them as gifts.

I really like mine from Crate & Barrel: http://www.crateandbarrel.com/reversible-jelli-boards/f48060

Yep, go Epicurean, they're great!

+1 for Ikea's Legitim cutting boards, they are dishwasher save, they don't bend after heat-drying and at $1.49 they are cheap to replace.

I like the Slice N Pour, it doesn't take up much space and it has a handy bowl on the side to hold chopped food. http://www.amazon.com/s/ref=nb_sb_ss_i_4_7?url=search-alias%3Daps&field-keywords=slice%20n%20pour <a style=""

Hmm...pretty much any? I mean, its personal preference for shape/size and all but if it's plastic, toss it in the dishwasher. I have cheapo Ikea ones I use just as much as nicer ones. Whatever is clean :)

I bought an Epicurian Composite board....LOVE IT!!! Its lightweight, durable, dishwasher safe and easy to cut on.

No help from this quarter, sorry. Never used anything but wood here. Just wanted to hop on & say I'm impressed with the number of helpful, respectful replies. How REFRESHING! =]