Mesmer is a GREAT secondary, cause every one of the 3 skill sets is useful to some profession.
As a monk, my favorite is inspiration, but the others are so good, i love to switch back and forth using all the skills and having fun with them. I REALLY like the inspired hex spell... not only does it remove a hex from an ally and gives you back extra energy, but for 20 seconds, you steal it and use it, whether you know it or not. I steal hexes all the time and turn it around on them... this really frustrates people and it works great on mobs too.
Imagine getting hit with a health degeneration hex (or some other nasty one), only to be removed, stolen and used back on your enemy, and I never even had it in my toolbar until I inspired it

. Heh.
Just one of MANY useful and fun tricks up the mesmer's sleeve.
Jana