Greetings and welcome to the game! Cache containers are only limited my the hider's imagination. While GC.com lists the "relative sizes" of each cache size category, there's a lot of variation in each. I've seen "small" micros and "large" regulars. The 2ml micro you mentioned was likely a "nano", not its own category (yet, see forum posts for requests and debates on this), which is most often magnetic and most often black in color. It's also commonly listed as the smallest geocache container (for now). Google "nano geocache containers" for a good idea on what these look like.
I've seen a few devilish containers. I won't go into these for fear of spoiling your fun, but let's just say that they looked pretty ordinary and certainly didn't look out of place at all. Remember, geocache hides reflect their hider's creativity, ingenuity, and skill at disguise and camouflage. The most interesting containers I've found were also the most memorable finds. Take that into account, as the hider's ability to hide something a little bit different and memorable is a great source of pride for them. Some local cachers will be a lot of help finding these (I found my first nano as part of a local group hunt, where the seasoned cachers had already seen probably dozens of them).
It might not help much, but I always try to think while out hunting "If it looks out of place, it might be the cache. If it doesn't look out of place, it might be the cache too!"
All the best and happy hunting!