We're a trading shop, so we've got users running two(or more machines) with at least two monitors connected to each machine. The traders demand that we only have one mouse and one keyboard for the entire installation. The current tools that we have are ok at best, and I was wondering if there was anything else out there to handle the problem.
I think Synergy might be what you are looking for. I love it. I use it at home to share a keyboard and mouse between my linux and windows boxes. I move my mouse cursor to the left side of the screen on my windows machine and it appears on the right side of the screen on my Linux box. No extra hardware needed if the two (or more) machines are networked.
If you want to control multiple computers with one keyboard/mouse in Windows I've used Synergy and Input Director and will only recommend Input Director. Synergy locked up and wouldn't let me mouse over to the slave when the master was pegged. ID has never failed me. Plus I find ID's copy/paste clipboard-syncing to work much better.
If you are a programmer and aren't intimidated by a fiendishly complex application, there's a powertool called WiLMa that can manage window layouts, create and restore them, move them around, and a lot more. I haven't figured it all out yet.
On each computer, to optimally use both monitors I recommend Ultramon. I use it on Dual-Monitors at work, and Hex-Monitors at home, and it's fantastic. I actually combine it with VirtualWin to get more desktops, and the iconized plugin mapped to the tick key (next to 1) to get 4 desktops of 6 monitors each, with handy little icons of every program running on each desktop.
Ultramon puts a taskbar on each monitor showing you only the windows on that monitor, lets you drag maximized windows around, set up different backgrounds/screensavers (if you're into that), shortcuts to throw windows to other monitors, maximize windows across monitors, and loads more. To me, it's an absolute necessity if I'm working with more than one monitor.
For multi-machine setups, Synergy is the way to go. One keyboard and mouse to control multiple machines, mouse pointers move smoothly from one window to another, and it allows all sorts of monitor arrangements.
I have 4 monitors on 2 machines (2 and 2) and on windows I use Input Director.
One alternative is a KVM box, of which there are thousands .. I have used the Belkin OmniView line.
You could also cheat, and have a primary system with lots of monitors and remote desktop or VNC into the other systems. This may be the easiest to manage overall, as only one has the non-standard hardware for multiple monitors.
I haven't used Synergy, but it looks interesting, and the GNU GPL allows commercial use.
EDIT: Thanks Berek for pointing out my lack of clarify. You would probably only use the K and M portions of the KVM devices.