The MGB suspension in good condition makes a rather nice handling car. The caster angle on the steering is a bit severe for modern tires, but it can be fixed with shims.
The key words here are "in good condition". The geometry of the front suspension is set by the design of the car, the only adjustment being toe-in. Needless to say, all the bushings need to be in perfect shape for the geometry to work. I only use polyurethane when rebuilding front ends. Generally, the color denotes the firmness. Black is the same hardness as stock rubber, red is firmer. Shocks must be perfect, nothing less will do. I use shocks rebuilt by Peter Caldwell, with delrin bushes and lip seals instead of the rubber discs that came on them.
A complete front end rebuild with shocks, kingpins, bushings and trunions goes for around $800, without any detail work, such as painting or powder-coating.
The next step up utilizes tube shocks instead of the lever-arm shocks. The stock shock is retained as a suspension link, but the valving is removed. Tube shock kits for the front range from $475 for Monroes up to $675 for Spax adjustables.
The ultimate front end for an MGB completely replaces the springs and shocks with a coil-over suspension system. These are completely adjustable for caster, camber, toe, ride height and shock valving.
One kit, from the MGOC costs £800 plus freight, as of this writing. Another kit from a US vendor is soon to be available. I have used the MGOC kit in several cars with excellent results. The sub-frame needs to be modified for clearance of the coil-spring, by cutting and welding in a small plate at either end.
Update: After having a coil-over shock fail internally, and being "shocked" at replacement cost for single units, I have sourced an American-made coil-over that will fit the MGOC suspension. These are "rebound valved" and adjustable, meaning the wheel can descend freely into dips in the road, and the shock will dampen the bounce, rather than try to stop the suspension from diving in the first place. These were developed for the street rod market and light weight of those cars translates very well to the handling characteristics of the MGB. A set of these has transformed the solid but somewhat harsh ride of the car in question to one just as solid, but much more smooth. The same design of shock is available for the rear as well.
A recent development involves replacing the steering rack with a power rack available from MGOC. I am not completely happy with the kit as it comes, but I have designed several modifications to the kit that makes it a superior installation, giving light, controlled steering, even with the fitment of wide tires. The kit costs £995, plus freight, and is available with either a mechanical pump for fitment on the engine, or a remote electrically-powered pump. My additions to the kit feature chrome-moly racing u-joints and a new shaft for extra clearance, and cost an additional $200.
Rear suspension can be either a well-built stock arrangement, or an improved versions thereof.
For improved handling of any MGB a panhard rod kit is a requirement. I get these from MGOC for £350, plus freight. These lock the rear end side-to-side and eliminate the "squat an roll" MGBs exhibit on hard cornering.
Tube shocks can be fitted as well and are one of the easiest way to improve B ride. Depending upon manufacturer, kits range from about $250 for fixed-rate hydraulic tubes to $500 for the adjustable, rebound-valved units mentioned above.
To do away with the problem of sagging leaf springs, one can either go the European route of mono-leaf parabolic springs for £200, or the modern option of composite springs. The last set I bought was $600. These are light and fast, and require the use of a tubular shock kit. I am generally unimpressed with new multi-leaf MGB springs, and would avoid them for spirited driving.
The final addition to rear suspension would be the fitment of a set of anti-tramp, or traction bars. These limit spring movement to the up-and-down plane and eliminate wind-up and wheel hopping in high-powered vehicles. They are available from several vendors for around $400.
While there are several folks offering independent rear suspensions for MGB, I really do not feel that the meager handling benefits offset the huge costs involved. I may be swayed in the future, if a reasonably-priced option becomes available, however.