just me talking here.. center first, since it carries the largest portion of the dialog in HT.
you're going to want to spend decent money on the sub. Your Titans will carry as decent bass as you would get with a cheap sub, so hold off on that for now.
you might want to get some minor-league rears at the same time as the center until you build up enough for the sub. The rears in an HT setup (notice the qualifier all you multi-channel audio guys about to jump all over this) should carry only mid-range and high stuff (as that is what gives you the impression of movement), so you can get some halfway decent sound movement without spending alot of dough.
if you are already heavy into SACD or DVD-audio, you will need good rears.
for under a hundred bucks (even wayyyy under a hundred) you can grab some indoor/outdoors that mount easily and carry good quality sound. try JR.com or etronics.com or even the new Rocket sereis I/O's at av123.com, all under a hundred. look for something with a main driver in the 4 to 5 1/2 inch range, since you don't want bass coming out of the rears. if nothing else, you are buying time until the new formats come out and you will have a better idea of what is needed to meet them.
bass is omnidirectional, so you don't gain anything by that coming from the rear speakers.
then get a decent sub.
It will let you experiment with placement and movement. Somewhere down the road, you can invest in quality surrounds for SACD/DVD-A needs.
just me talking.
