Look at your current usage and double it at least, triple is even better because coming half way through the month and running out of bandwidth is probable the worst thing you can do for your website, your users will probable desert you, if they see it isn’t online for a day or two.
Nice VPS solutions you can get from
Regvps.com and
Rockhoster.com web hosts.
The abundance of good feedbacks about these web hosts makes it the most preferable.