Actually, no. Illusionary techniques ARE genjutsu, that's the meaning of the word.there is only a fine line between genjutsu and ninjutsu. illusionary techniques are part of the magical techniques (ninjutsus).
Ninjutsu are elemental techniques, or those with physical results. Sasuke's fire elements are ninjutsu, as is his chidori. The various earth, fire, water and forest jutsu used in the Hokage battle are ninjutsu. Summoning techniques are ninjutsu. Naruto's kage bunshin is ninjutsu, because the clones are physical, and can strike and be felt when you hit them. The academy-level bunshin no jutsu is a genjutsu (illusion); they are just after-images, and if you look closely you can tell the difference between them. (Recall the Sakura-Ino fight.) They are not physical like Naruto's clones.
There has been some debate over whether Henge (transformation) no jutsu is nin- or genjutsu. If it was a genjutsu-based illusion, it would not be a physical transformation. However, I believe that when Sasuke throws the windmill-shuriken-Naruto at Zabuza, he proves that Henge is actually a ninjutsu, physical transformation; I highly doubt Sasuke could actually hurl the real Naruto like a windmill shuriken.
Main, kick-ass genjutsu used in the anime thus far are: (most have already been mentioned) the technique used by Kabuto with the falling feathers that puts the crowd to sleep; the Bringer of Darkness used by the 2nd Hokage (First in the manga), and the series of genjutsu used by the Mist-nin trio in the Forest of Death against Team 7 + Kabuto.
Actually, that technique used by the Mist-nins is a great example of the difference. Their clones are simple illusions: the real ninjas had to hide out and match the trajectories of the illusionary weapons with their own weapons, otherwise the illusionary weapons would pass right through and Team 7 would quickly have figured out the game. Had they been shadow clones like Naruto uses, the weapons thrown could have been solid. Also, the sharingan sees through genjutsu: when Sasuke looks at the illusionary clones, he sees not people but an outline with a glowing blob of chakra in the middle.
Quick way to tell the difference: You can touch it, or physically feel the results (I sure wouldn't want to touch the chidori!) = ninjutsu. You can see it, but can't touch it = genjutsu.