4GB cards getting rare. 8GB seems to be the small card of choice at Staple, OfficeMax, Best Buy. Price as low as $4.95 for Kingston 8 GB SDHC, Class 4.
http://www.bestbuy.com/site/kingston-8-gb-secure-digital-high-capacity-sdhc-1-card-blue/1304811927.p?id=mp1304811927&skuId=1304811927
4GB in MicroSD - too easy to lose them if handling a lot, and then need an SD adapter anyway to read on most PCs equipped with a reader. Good if just going to plug in & leave it, like a cell phone.