"A man, a plan, a canal...Panama!" (21 letters) is one of my favourites. And here's another..."Norma is as selfless as I am, Ron." (25 letters) That one - like the first - has the inestimable advantage of being a) easily punctuated...b) in standard English...and c) perfectly sensible.
Many so-called palindromes found on websites etc are merely collections of words that make little, if any, real sense or are not in �normal' English. Without sense and normality there is little point in creating palindromes. Here's the sort of thing I mean..."Nedra Olso is in Oslo, Arden" or "Unglad I tar a tidal gnu."