If you don't need input to output ground isolation, go for a simple buck converter, this will avoid complexity and save time. If ground isolation is required, you would have to go for a transformer coupled topology, and for 2A I recommend either flyback or forward topologies rather than full bridge because they use just a single primary side switch and one or two secondary side diodes.
Both 1 and 2, above, can automatically design several different suitable SMPSs for you, using the SMPS controller ICs of either National Semiconductor (1) or Linear Technology Corp (2). I would try both of them.
I have not used National's Webench, but I can vouch for the Linear Technologies simulator. Not mentioned is that it does analog simulations very well and there is a LT Spice users group on Yahoo that even offers vacuum tube models.
The underlying engine in the LT Spice simulator is Pspice.