When I hear someone say "This poem is untitled" I shudder- visibly- titles are important! As far as I'm concerned, it's as least as important as what you name your kids (Paul and Alia).
I know someone who has a small book where the poems are numbered- I gotta tell ya, thumbing through the damned thing looking for one I liked particularly is annoying- I don't think I've read it since the first two or three times, it's so frustrating.
Here's some thoughts on titles from Ross White (the numbers are mine)
1. Your poem's title is like the first jab in a boxing match-- you don't have to knock the reader out, but you had better establish yourself as a formidable presence in the ring. A poem which is sharp, precise, and economical deserves a title to match. Sloppy, awkward, and abstract titles always raise the hairs on the back of my neck. Tight, concrete titles that locate me immediately in what is happening in the poem make me happy.
2. If there's a clunky detail in your first stanza, it might be information that could be better conveyed to the reader in the title. Excess narrative information in the body of a poem, particularly early, irritates me-- because they suck the poetry out of the poem. Titles that convey that information in a plain style remove the burden of exposition. Specific dates, locations, or people show up in titles for this reason.
3. Nobody wants to be told what to feel. People want the emotional stakes of the poem to be earned. So, if the poem is titled "Happiness" and goes on to describe happiness, that's pretty lame. If the poem is titled "Happiness" and goes on to challenge the reader's perception of happiness, carry on.
4. Don't make every title the same. Pearl Jam's first album has eleven songs, right? But take a look at the track list, and it's mind-numbingly similar. When titling a poem, look at your related work, and see if you have any nasty habits when titling. If you find that every title is one word, or includes the setting of the poem, or is a borrowed line from Plath, vary it up. (It's worth noting that, if you are looking at manuscript shapes, and you find a conscious and strongly patterned repetitive urge, that's worth exploring. You may not want to ditch it too soon.)
5. A simple title can plug your poem into a much larger tradition very quickly. "Aubade" or "Alba" says a lot. (A funny aside-- Wikipedia lists Eagle Eye Cherry's crappy song "Save Tonight" as a modern example of aubade. Apparently, aside from one Philip Larkin poem, there are no other possible examples. This is what I get for being so fascinated with Wikipedia.)
6. Don't telegraph the end of the poem in the title. I hate to be the guy who gives examples from his own work, but here's one: if you're going to have the speaker disappear at the end of the poem, a title like "Disappearing Act" or "The Vanishing" might announce your intention a little too much.