wyo diver,
for me there are 3 major issues with masks:
air volume, field of view, fit.
air volume
the smaller the volume of the mask the less air you need to equalize your mask as you descend, which means you have more air in your lungs (definitely an important consideration for freedifing). scuba masks tend to have high volume as there is no real limit to air for equilizing the mask as you descend; although they have recently started to produce lower volume scuba masks as well (not sure if they are low to the same extent as freediving/spearfishing masks though). additionally, the lower the volume of air in the masks generally the less drag created in the water. for example, in the pool i was surprised to notice how much more drag my low volume alien mask creates than my swim goggles (i expect a large volume scuba mask creates substantially more drag than the alien mask)
field of view
small air volume, however, often is a trade-off with field of view. extremely small volume masks designed for high performance freediving (usually diving up and down on a measured line) do not have extremely wide field of view, which is not really necessary in this type of diving anyway (eg, omer abyss, cressi minima). there are some spearfishing masks, such as the omer alien or cressi matrix, that have a fairly small volume but still maintain a wide field of view (wide field of view is important in spearfishing or recreational freediving).
fit
all masks seem to fit differently so read through the forum and see how a particular mask fits (eg., some are designed for smaller faces). if a mask doesn't fit well you will have problems with leaks and/or be uncomfortable. some masks have a very flexible silicone skirt, which makes them both comfortable and fit a wide variety of face types (the alien is one example).
also there is the sphera mask (see swimm2000.com in the "other goggles" section), which has a low volume and an extremely wide field of view, however the fit is a little more finicky than the alien and i have heard they only last about a season before the seals go (i just got mine and haven't used it yet as the visibility in the water has been very low anyway).
personally, to get started i bought the black freediving package from spearfishinggear.com, which consists of an omer alien mask (low volume and wide field of vision), omer zoom snorkel (a flexible j-type snorkel--fairly standard and works quite well), omer black millenium fins (very durable and blades can be changed), omer socks (have open-cell neoprene cuffs on the ankles which seal well with my wetsuit). i am very happy with all of the gear so far---also it suited my recreational freediving needs well.
one other thing about snorkels is that some freedivers prefer rigid tube j-snorkels, which they leave on the surface (attached to a float) when they dive (i presume this is for hydrodynamic reasons). the rigid tube allows the snorkel to stay out of the water without having to be attached to your mask during breathe-up. most recreational freedivers/spearfishers tend to keep their snorkels attached to their masks as they may not surface at the point they dove (and left their snorkel).
also you will need a rubber weight belt to hold your weights, which will stay tight around your hips even as you descend and your wetsuit compresses at depth. finding the right weight will depend upon many factors including the thickness of your wetsuit, your style and depth of diving and personal preference --- but it will take some experimenting with different amounts to find the right balance. refer to some recent threads for weighting info (eg. the link below).
generally, with any piece of gear for freediving you will be able to find threads detailing people's hands-on experience. prior to any gear purchase be sure to make good use of the deeperblue search function and ask questions if you can't find what you need.
also check out these recent threads discussing freediving equipment:
http://forums.deeperblue.net/freediving-equipment/72493-what-equipment.html
http://forums.deeperblue.net/beginner-freediving/72851-how-much-weight-vancouver.html
this is an excellent thread as well which covers a whole bunch of freediving topics - great info to get started:
http://forums.deeperblue.net/beginner-freediving/64959-how-start-freediving.html
cheers,
sean
vancouver, canada
edit - to add snorkel and weight belt info