Was in the market for a single memory foam mattress, and came across Ergoflex. Ergoflex aims to compete directly with Tempur, which is the gold standard in memory foam. Contrary to cheap memory foam mattresses, Ergoflex makes them to the same specs as Tempur, and provides a 10 year warranty. The reviews are excellent:
I came across a coupon on www.ozdiscount.com for free shipping, which saved me $100 (strangely enough that coupon disappeared from Ozdiscount, but it still works).
I received the mattress yesterday (<7 days to WA - faster than Australia Post), and can say it feels very similar if not the same as the Tempur I normally sleep on. It is much cheaper, however. Pity I did not know about Ergoflex 2 years ago.
For those not in the know about memory foam mattresses: they shape according to your body, but provide better support than normal foam. The Ergoflex matresses use the same memory foam density as Tempur (85kg/m3), contrary to all the cheapies out there. See Ergoflex's sales explanation. Memory foam is very good for (most) people with back problems.
Ergoflex has a "sale" (which they have very often), but the free shipping saves you between $60-$130, making it a real bargain.
Prices
Single - $499
Long Single - $549
King Single - $599
Double - $799
Queen - $999
King - $1199
Have found mine to be really good! Their customer support is excellent too