I've been using this SanDisk Extreme Pro UHS-I 45 MB/s card SanDisk Extreme Pro 16GB (SDHC) 45MB/s UHS-1 Card
in my lowly E-PL1 for several weeks now and it's performed flawlessly. I previously used this same card for 3 months in a big Canon T3i DSLR. To use it in the E-PL1 I simply inserted it and hit the Format button. I've also used a SanDisk Class 10 card in both cameras without problems. The class 10 seems sufficient and the UHS-I my be overkill.