Use your illusion II
Level 5- While the SC gives us the Illusionist means of quick travel with shadow fade, and the PHBII gives us the classic friend to foe spell allowing the illusionist to manipulate the battlefield. A very utilitarian spell is the PHB’s shadow evocation. Consider it like a mini-wish, yes the 20% effect with a failed will save can diminish the potency but the versatility of choosing any evocation spell is pretty handy. The enemy is in that perfect straight line which is perfect for a lightning bolt but you don’t have that spell… you could really use a gust of wind at that moment to push the blackguard of the cliff.. you got it.
Level 6- While distraction is the illusionist’s forte, mislead is the perfect combination of magics wrapped into a tight bundle. You create an illusionary copy of yourself, while at the same time placing yourself in greater invisibility. You could have the double perform a variety of tasks, such as attempt diplomacy, or pretend to cast a spell (then vanish), while you place yourself in the perfect spot for further spell casting all while remaining invisible. Not to mention many enemies want to open up with their most effective attacks on a spell-caster and with this spell, they would be likely to waste it on your illusionary double.
Level 7- If you are an illusionist who can cast simulacrum you can create the army of icy copies of doom! When you kill that mighty red dragon, why not make a half hit die copy, which is at your beck and call (Or how about half a dozen). Or a couple of half powered doppelgangers of yourself which can buff you for combat before casting invisibility on themselves and making their way to safety. The possibilities for this spell are really quite endless.
Level 8- Just when your DM has squashed greater invisibility antics with a bunch of see invisibility endowed enemies now comes the paramount invisibility, superior invisibility (SC). The end all be all of invisibility. It prevents detecting the character through any other weird sense, scent, tremors etc. and is not subject to the see invisible spell. So once again, your illusionist can reign spells down upon their enemies while being completely cloaked.
Level 9- The top tier of magic does not present us with many options for illusion. At first glance weird seems like an aoe version of phantasmal killer, which is not too bad.. but then again not seemingly earth shattering until you look at the target area, “Any number of creatures, which cannot be more than 30 feet apart.” When put to practical use this is a pretty frightening concept… you know that army of 10,000 bugbears seeking to level the capital city, well now they all must make a save or die. Imagine if cast in a city environment? How many targets can be chained 30 feet apart? In a small dungeon, every encounter could be less than 30 feet apart and they would have to confront their greatest fear or die. For mass slaughter, few spells do better than weird. Meteor swarm may be flashier but then you have to worry about catching allies and collateral damage, weird is surgical. It allows the caster to choose who in the area will be subject to a horrific death on a biblical scale.
Overall- Illusion is a school of magic that really is as useful as the player is crafty. While party members might berate the illusionist for his lack of magic firepower, the right illusion can be a party saver. The right spell for the right situation is always a subject of circumstance. What the spells above illustrate are some illusion spells will make the illusionist much more than just a source of distraction, but a master of fear, shadow, and deception.