After reviewing the options in the help section of their website, it doesn't appear that you can adjust the download speed of Download Accelerator Plus. If so, this is a serious fault, especially for those with limited bandwidth.
I use Mass Downloader
and am very satisfied with its performance. It's a full featured download utility with all of the options you could expect including download speed control. It has four different speed settings which can be manually set to the desired download bandwidth. It's a good program for $19.95 U.S., and doesn't load any spyware like some other download programs (i.e., DAP).
MetaProducts also has Download Express
, which is a free download manager. It does most of the essential things, such as resume downloads and manually control download speed. It's fast and allows multi-thread downloads (no spyware). I use it for my default download manager (it automatically replaces the Windows downloader) unless I want to queue multiple files, in which case I use Mass Downloader.
FlashGet and GetRight also allow manual adjustment of download speeds.