Although I don't particularly like recommending them.. Tesco have currently got some TDK branded 4Gb SD high capacity memory cards for £9.99
Price is somewhat better than you'd pay for an equivalent Sandisk card, but a little bit more that you'd pay someone like 7DayShop for a random brand.
I can't find any specs on the cards at the moment (TDK Europe's website appears to deny that they sell them!), but performance seems comparable with other cards.
If I recall correctly, Tesco also have 4Gb USB plug-in memory cards for a similar price.
Hello again darkness, my old friend...