I find that (in 4e anyway) there's really no reason not to multiclass. A multiclass feat is basically a skill training feat with some bells and whistles attached.
Now, if you're planning on actually buying some power-swap feats, then obviously you need to be a little more careful in your consideration.
It's tough to say without seeing your particular stat array, but Warlord seems a decent choice. You can take advantage of your good Strength and Charisma that way. If your Charisma is really good, as high or higher than your Wisdom or Strength (which would be unusual, but not impossible, for a Cleric), then you can considering multi-classing to Warlock (Star Pact or Fey Pact, obviously).
Paladin might be good too. If you find yourself tanking a fair amount already, a once-per-encounter Divine Challenge will improve with that. I've never quite liked the multi-class Fighter feat... a +1 to a single attack and the ability to mark a single foe once per encounter just isn't worth your one and only multiclass, I don't think.
One of my personal favorites for a Cleric is Ranger, though. Hunter's Quarry gives a little bit of a Striker-like edge against a single opponent. More importantly, you can use it to get training in Nature, and easily expand your repetoire of rituals. Finally, your high Wisdom will synch up nicely with some Ranger powers, provided you have the Strength to hit with them.
