DM'ing for a swordmage can be pretty annoying. They have a lot of interrupts, and leave you high and dry abilities. But that's why you build redundancy into your encounters. Fighters can sometimes do similar lock downs too. And that just means they are doing their jobs. I find it's usually best to suffer the consequences of whatever it is those defenders are doing, and make your best move.
If it means the Swordmage gets to teleport out of the trap, fine, the trap might have failed anyway. If you take a combat challenge attack from the fighter to shift to a position where you can blast the whole party, just suffer the attack. So the monster takes a bit of damage. Monsters have nice pools of hit points precisely for this reason.
If a monster needs to take an opportunity attack from the rogue so it can go flank the rogue, make it happen. Taking some damage is well worth a +2 to hit. Dealing flanking skirmisher damage on a rogue and maybe knocking them down or dazing them is well worth the 8-10 points you took from the free attack.
Monster tactics are quite a bit different than PC tactics because they have different resources, the biggest one of which is their HP's. So I try to use that resource to press the PC's into difficult positions, where even if the outcome of the battle highly favors the PC's, they feel like they are in a tight spot and must use encounter/daily powers to get themselves out of the jam they are in.
Monsters have one major goal, to wear the PC's down before their next fight. So sometimes an intelligent nemesis, might observe the party warlord was severely wounded in a fight, and send an assassin/lurker after the warlord. This might be a quick fight for the party as they speedily dispatch the assassin, but if it does some serious damage to the warlord before it goes down, running him out of surges, the party will have to be very careful not to expose their leader in future fights, so the warlord may no longer be as effective.
There are lots of ways to keep players threatened. You just have to come to terms with the fact that the first encounter of the day, is not likely to be the one that sends the party running home, unless you seriously increase the threat level.