Honestly, any place with a fast spawn or a loop with enemies around lv.45 is good. One of the most popular spots for spiritbind is Urth's Gift in South Shroud.

As for the kind of materia you want to get, that will vary depending on the marketboards. Most crafter and gatherer materia will sell well, as will det and crit. If you have a 50 goldsmith available, keep some electrum ingots and jewels around for a quick hq craft. HQ items sb faster, as does melding junk materia to them (Fire, Wind, etc). You will want ilv.45 or ilv.55 items to spiritbind as those will yield rank3 and rank4 materia.