It depends on how much traffic you plan to serve and how complex your sites are.
I currently manage a VPS1 account at LW (and personally have a VPS2). With all services (Apache/Exim/MySQL/CPanel/etc...) up and running on the VPS1 and a small amount of traffic, it is currently using 287MB of RAM.
The VPS does have a PHP cache taking up 32MB or so of RAM, and it gets a reasonable amount of mail traffic.
If you are running only 1 site or a few smaller sites (without huge traffic requirements) it should be fine. Otherwise, get a VPS2.