I like Vanguard's Target Retirement funds. They don't stack fees, so you don't pay any more fees than you would if you built the portfolio yourself (I remember doing the calculation once, and the fees charged for the fund pretty much equal the fees charged to the component funds, in the allocated proportion).
It's a great place to start investing, because you can save on account maintenance fees and low balance fees when you're just starting out, i.e. it's cheaper to hold one fund with 10K in a target retirement fund rather than 4 funds of 2,500 each. As your assets grow this of course becomes less of a factor, but it's worth pointing out.
The automatic asset allocation is great for two reasons:
(1) your asset allocation will get more conservative over the years, as it should, even if you're lazy (or even if you're star-struck by great stock market returns); if people followed the simple advice about moving to a more conservative portfolio as they approach retirement, we wouldn't hear a gazillion sob stories every time the market crashes and another crop of 64 year olds suddenly realize that being 100% invested in the stock market is not a good idea
(2) it keeps your asset allocation in line even in the face of a tanking stock market, as happened last year; many people (myself included) who otherwise would not have had the guts to sell bonds and buy more stock when the market tanked were able to do so because the target funds automatically rebalance during market swings
All in all, it's really a solid investment for lots of reasons.