Also Kingston 4Gb miniSDHC, class 4 (£17.44 including delivery).

~ $ sync; time sh -c "dd if=/dev/zero of=/media/mmc1/testfile bs=1M count=100; sync"
100+0 records in
100+0 records out
real 0m 31.29s
user 0m 0.02s
sys 0m 2.23s
~ $ time dd if=/media/mmc1/testfile of=/dev/null bs=1M
100+0 records in
100+0 records out
real 0m 15.45s
user 0m 0.00s
sys 0m 1.80s

N.B. All times are best of 3 runs.