Please be sure to read the description of the expansion tank before you order, some boiler expansion tanks look identical but are not interchangeable.
Please see my page on expansion tanks.

Amtrol 15 Expansion tank This is a small expansion tank that screws into any 1/2" iron pipe size fitting but will not screw into a Fill-Trol valve. Height: 12 5/8" Diameter 8" Volume 2 Gallons. This expansion tank is good for small residential boilers. $53.99

Fill-Trol 109
Expansion tank

Although this expansion tank looks smaller then the # 15 it is the exact same size but they are not interchangeable. This tank will only fit into the Fill-Trol fitting above the tank in the picture. Tank comes with brass fill-Trol valve.
$102.49   

Amtrol 30
Expansion Tank

This # 30 expansion is the most common used on residential boilers. Like the 15 it will screw into any 1/2" iron pipe size thread.
Height 15-1/2"
Diameter 11"
Volume 4.4 Gallons.
$58.99   

Fill-Trol 110
Expansion Tank

The Fill-Trol 110 is the exact same size as the #30 expansion tank but is not interchangeable. This tank will only screw into the brass fill-Trol fitting seen above. The brass Fill-Trol fitting comes with this tank.

$129.99  

Amtrol 60
Expansion Tank

The number 60 Expansion tank is for larger residential boilers
Height 23"
Diameter 11"
Volume 7.6 Gallons

$98.25  

Amtrol 90
Expansion Tank

The 90 Expansion tank is for even larger homes or small apartment buildings.
Height 21"
Diameter 15-3/8"
Volume 14 Gallons.

$138.76