Here's a +1 for West and System 3. VERY good products, and a wide variety of hardeners - so by purchasing a couple of different hardeners, your large container of resin can be used with a variety of curing times.
And even though you have to buy them in large quantities, they're cheaper on a per-ounce basis than most hardware-store epoxies. Many places give good deal on the gallon size, but rip you off on the quart size (charging almost what a gallon would cost!). However, I've found local boat stores that sell the quarts of resin at a very good price.
In a former life (or so it seems), I did high-power rocketry, and used the stuff to lay up fiberglass airframes. Awesome stuff.
Also, you can somewhat extend the working life of any epoxy by keeping it cold, just like you can accelerate the cure by heating it up.