Transcend 16 GB SDHC Class 6 Flash Memory Card TS16GSDHC6is being sold on Amazon for around $42. I can remember the days of paying well over $100 for a one-gigabyte CF (Compact Flash) card. Imagine getting 16x the storage capacity for less than half the price, pretty amazing. And from what I've read, capacity is going to grow even higher.
The question this brings up, however, is just how big a card (or cards) you should use. My personal philosophy is that you're far better off with two or three smaller cards than one giant card. Why? For one, while I've only had one card corrupt on me (out of about 50 cards--and that was years ago), I suppose it is possible. How horrific would it be if your 32 gig card suddenly corrupted two days into a three week trip and you had no backups? I'd sooner have four 8 gig cards and have to change cards (which takes what--five seconds?) a few times during the trip. But more important is the question of losing a card. If you go to Africa on safari and put all of your images on one or two 32 gig cards and you lose one of those cards you've potentially lost (as we learned above) 10,000 pictures. Trust me, at that point you'll be feeding yourself to the lions voluntarily. You might still lose a lot of images even if you lost a smaller-capacity card, but you probably would not lose your entire vacation shoot.
Knowing how much card capacity you need is really a matter of how many megapixels your camera uses and what image-format you are using. If you shoot in jpeg you'll get a lot more images than if you shoot in RAW which is very memory hungry. You'll need a lot more memory if you are shooting RAW and jpeg simultaneously (as I occasionally do)? Also, do you shoot HD video with your DSLR? Video uses a ton of memory. There is a handy little card-capacity chart on the Lexar site (I wish it was bigger and easier to print out, but it's a useful chart) that will tell you how many images you can expect to record based on card size and your camera's megapixel count. I would consult the site of the specific brand of card you're using, too, because the capacity can vary slightly from brand to brand.
The bottom line is that what's true for eggs is also true for digital images: don't put them all in one basket and you'll feel a lot more secure about getting home with those digital eggs intact.