This has been discussed in length in various places, but here's a thread to start with: http://forums.fishusa.com/marcum_or_vex/m_144953/tm.htm
As for me, I own a vexilar fl-8 slt, a new this year marcum lx-5, and an OVS (precursor to Marcum) underwater camera. I love the vex and the marcum...wouldn't fish without one or the other. The marcum has some nice new features like adjustable zoom windows anywhere in the water column, and a few others. Is it worth the $550 price tag? It's too soon for me to make the judgement, but I really like what I see so far. Another option to consider is the marcum lx-3tc...nice units and have nearly all the bells and whistles the lx-5 has. The new vex fl12 and fl20's look pretty sweet as well. I have no first hand experience with either the new humminbird or showdown units.
The bottom line is: I don't think you can go wrong with either a vex or marcum flasher, and I don't think you necessarily have to spend $500 to get a good unit either.
On the other hand, the camera was largely a waste of my money...it's been nice on a few occasions to scout new water or to keep my kids occupied, but I tend to spend more time monkeying around with the camera than I do actually fishing. In addition, on most of the lakes I fish, the water is too murky to see clearly, especially with heavy snow cover blocking out the ambient light.
Just my opinions...hope I helped.