I use a Verbatim 32GB Class 6 SDHC Card as my main card (all of my apps and games are on there, and I tend to use it for written work as well, amongst other things), and an assortment of Play.com own-brand Class 4 16GB ones for music and DVD rips, and whatever else my main card doesn't cover, myself.
As Anihil8ion2199, PokitFoxx, and Blue Protoman alluded to (honestly guys, do we need to invest in a Prometheus-light, now?
), you should avoid eBay at all costs, as it is flooded with fake-capacity cards - a number of which are also counterfeits of brand-name goods, as well. It's worth noting that eBay is not the sole place affected by this - they have been known to pop up with third-parties selling via well-known online retailers as well (although this is not always the case, I would advise caution). The most extensive source of information on this unpleasant phenomenon is the website
SOSFakeFlash, although I wrote a run-down of the problem and of some related issues that surround it,
in a thread on this forum, too. Please give at least the latter link a read before investing in any cards.