How high is your terrarium (between light and ground that is). It also depends on your ambient temperatures, if it's now 22 C there and you wish to have 28 C then I would say you'd need a 75W light. If they sell only Exo Terra there, then I think this one will do the trick. If the space between light and snake is low (< 30 cm) then perhaps a 50W would be a better choice. You'll have to work it out a little bit, which works best for you.
These come in 25, 50, 75, and 100 Watt editions:
It says it's a spot light, but actually it's a flood light (65 degree beam angle). It does it's job alright, it's not too bright and has UVa light as well.
Try not to use real spot lights, they get too hot in the spot area and too cold everywhere else.