Here are some of the tools I use. I am always looking for new ones but it isn't so much to tool as what you do with it. X-acto type blades can be found all over the place and don't cost much and do a great job. There are any number of good holders for them. Probably my favorite flat blade is the Testors hobby knife but from what I hear they no longer make these. You can still find them in some stores in the model toy supply section. They have a really nice tip to them and hold and edge quite well.
There are a number of gouge blades out there. The most popular being the Speedball linoleum cutters. They come in various sizes. No. 1 - Liner, No. 2 - V-shaped gouge, No. 3 - Large Liner, No. 4 - U-shaped gouge, No. 5 - Large gouge, No. 6 - Knife. Most of the time you get them in a kit containing a handle and several cutters.
Another interesting product that Speedball sells are the Linozip cutters. these have the blade in a hook and one cuts by pulling the tool toward you instead of pushing it into the material as you would a gouge tool. You can see one on the far right of the second photo. These come in four sizes: No. 21 - Liner, No. 22 - V-shaped gouge, No. 23 - Large liner, No. 25 - Large gouge.
The most important thing is to use a sharp tool. It makes your cuts much better and causes less effort to cut the blocks. So look around your house and see what you have. There are a number or places to purchase gouge tools. Most local craft stores will have them and you can order them online if you are in a remote location.