Almost every major city has multiple plastic surgeons offering a variety of "penile enlargement" surgeries. The most common form of this surgery is suspensory ligament cutting -- this doesn't actually increase the size of the penis, but it does allow more of the penis to reside outside of the body, giving the effect of an extra inch or two of length. Girth is not affected.
In increase girth, several procedures are available. The simplest is fat injection, where liquefied fat cells are injected under the skin of the penis in the same way that silicone would be. Even though fat injection is a relatively safe procedure, the tradeoff is that only about 1/3 of the cells usually survive. This procedure will only enhance the shaft and has no effect on the glans (or on length). Only a thin layer is generally injected, but the procedure may be repeated for desired effect.
The other method of increasing girth is dermal fat grafting, where strips of skin with fat attached are surgically grafted to the penis. The survival rate for the fat is much better than with fat injection, but there is scarring on both the donor and recipient locations.
Penis stretcher devices or penis extenders are devices designed to apply continuous stretching force. Penis stretcher devices apply traction via bars between an anatomically curved base that fits at the root of the penis, and a band that slips off the head of the penis.
Some homemade devices are also used. The most common design is two plates with long screw/bolts holding them apart. By turning these screws, the distance between the two ends can be altered. The one end is held to the body by pressure, and the other end is attached to the glans of the penis by piercings or a loop around the corona, or in the case of a scrotal stretcher, the end plate may simply have a hole in it through which the testicles are inserted as a backing.
Other devices include elastic/bungy contraptions where one end straps to the leg and the other end straps to the genitals.
The internal structures of the penis can easily be damaged by overstretching, resulting in a long but impotent penis.