Are you just trying to make it look prettier? After it's all done you can probably use any sort of spray clear-coat on the solder side, but I wouldn't do that before soldering on components. There are some spray-on coatings that serve as flux (http://www.lpkfusa.com/Store/ProductDetail.asp?ProductID=107
) plus LOTS of special-purpose "conformal coatings" designed to protect PCBs from all sorts of highly specified environmental "issues", but they tend to be very expensive.
There are also assorted products for tin-plating your PCB.
Frankly, if you're going to solder your board relatively soon after making it, I don't think any of these are worth the trouble. While the copper traces will oxidize on the surface, the oxide is a bit like Aluminum oxide - it's protective of the remaining copper, and the PCB will stay in working condition for decades (while at least one of the tin plating products I was looking up contains exactly the sort of fluxes that you are NOT supposed to used on electronics...) It'll just look not so pretty...
I don't think I've ever seen a home fabrication friendly soldermask material that actually works as a soldermask (ie holds up to soldering heat on nearby parts of the trace.) THAT I'd like to find (I think "real" soldermasks tend to be 'cured' epoxy-like things, nasty and difficult to deal with in home environments...)