There are a few tools essential to kitchen cookery that are going to take up up a bit more space, I'm afraid. The more I cook, the more uses I find for them, though. Once I learn a new trick, I wonder why I never used them that way before.
It's pretty handy to have two of these things, one large, one small. A good sieve can be used for more than sifting dry ingredients, or straining wet ones. They can stand in for a food mill, pureeing cooked fruit and vegetables by pushing the food through with a spoon. This gives pureed soups a super silky texture.
I like free standing colanders with lots of small holes and large handles. They make it easy to safely drain the liquid from hot pasta, boiled vegetables, and beans. I just put the colander in the sink right over the disposal, and dump in the cooked food. With beans, I pull out my trust kitchen sprayer and rinse them off, right in the colander, after cooking.
Can you ever have enough mixing bowls? I've got five that I use for this sort of thing and sometimes I still wonder if I have enough. Get plenty of different sizes that can be fit, one into another, so that they can be more easily stored, only taking up as much space as the largest one. Glass is probably the most versatile, and certainly makes it easier to see all around if you've mixed every thing up well. Glass can more easily break, if dropped, though. Stainless steel or sturdy heat resistant plastic will do nicely. If can, get some that have lids that will fit tightly over the top. That way they can also be used to store leftovers in the refrigerator.
Recently I've started using my large sieve in combination with a large mixing bowl to rinse rice or lentils. I put the rice in a large sieve and then put the sieve in a large bowl. I run water over the rice, swirling the rice around. As the bowl fills with water, it's like giving the rice a bath. Change the water out two or three times and you've got amazingly washed rice. I've never been able to get as much of the starch and rice powder off the rice before. My rice is so much fluffier now!