The only reliable place where I've found a 32GB microSD card (of any class) in stock has been through Verizon directly. I picked up a 32GB SanDisk class 2 when they were running their special ($100, or $75 with corporate discount).
The class specifies the minimum write speed (not read). A class 2 should have a min write speed of 2 MB/s, while a class 4 should have a min write speed of 4 MB/s. It's quite possible to have a class 2 card outperform a class 4 card, but usually the higher class the card the faster the write.
FWIW, I ran hwtest on my default 16GB SanDisk class 2 (my X didn't come with a class 4) and compared it to the 32GB SanDisk.
16gb Sandisk class 2
Writing speed: 3.85 MByte/s
Reading speed: 13.2 MByte/s
32gb Sandisk class 2
Writing speed: 5.37 MByte/s
Reading speed: 13.5 MByte/s
Note that while both are rated class 2, my 32GB actually performs faster and is well above a class 4 minimum write. YMMV.
Glue is right: for most purposes, including the 720p HD recording on the X, a class 2 card is fine.