Aptitude is a very useful curses-based front end to the apt toolset. It is generally considered better than dselect and has features like multithreading, the ability to undo changes and you can even play minesweeper while you are downloading.
See also: Synaptic
'Could not lock the cache file'
If you don't close aptitude properly, it might not delete the locks it has created. This would result in that next time you use it you get an "Could not lock the cache file" error. On Debian this can be fixed by removing the locks:
If the above does still not help, you most probably interrupted aptitude and therefore dpkg during the configuration phase. If so, or as a last resort, try issuing this:
dpkg --configure -a