As Norway said, there are a number of minor things that will be impacted, but reputation (deeds) is more important in BG2 than alignment (philosophy). Among the trivia to watch out for:
*some weapons can only by used by characters of good alignment, some by those of evil align.
*store prices vary by rep., not align.
*Undead, when turned, react differently to evil clerics than they do to good clerics
*at least one romance mod. is align. sensitive, as well as race sensitive
The real issue if you are so deep into role playing that you bothered changeing align. is that the game pushes you into doing "good" deeds. If you have surrounded yourself with an evil party, as your reputation improves they will start bitterly complaining and if it becomes angelic, will leave you. Similarly, your good NPCs will quit if your rep. sinks too low. Also, a very low rep. party will find itself constantly attacked by "vigilantees", as well as overcharged by merchants. So, an evil group has to watch its rep. closely and give to the church (Up) or rob isolated "widows and orphans" (Down) to keep things comfortable.
Being Evil on Toril is hard work!