Need new server advice, please

[attroll]

I am in desperate need of some advice on purchasing a new server for my sites.

Here are what my current server consist of;

2x INTEL XEON 5345 2.33GHZ 1333MHZ FSB 8MB QUAD CORE
4x 2048MB Memory giving us a total of 8GB of memory
4x 250GB 16MB hard drive setup as raid 10 = 500GB
1 TB as a backup drive
1x 250GB 16MB as a spare drive

I am running three VBulletin web sites on this server now.
Two of these sites are fairly large, which have outgrown the current server. This is the reason for needing to purchase another server. The server is getting sluggish and slow.

I would like to move all the sites to the new server. I would rather not maintain two servers.
I would like something that the sites can grow on. I really do not want something I will outgrow again soon.
I want something that will be able to handle a large load and have fast response times for my users.
I would also like expandability if possible.
I do not have a ton of money to spend either but I need something better then what I have now.

I am open to advice and suggestion, PLEASE.

[snakes1100]

Help if we knew a budget

[attroll]

I think I have this problem resolved. I did an optimization of the server and that seems to have helped.