Depends way you mean by decent but I get mine done at a small place right in the old town in the Avenida 25 de Abril opposite the multi-storey car park. Costs 9 Euros, a good job. One of the barbers speaks English, the other does not.

There are a couple of others also in the old town, don't know about the rest of the area.

Thanks Cubsur. Don't want haircut after hols as thats just shows us the bits that didn't get tanned due to long(ish) hair.

It occurred to me I didn't say the name of the place then I realised I couldn't remember! It's Salao Rijao or something like that.