Can you recommend a business class modem/router?

My school needs to replace our router for our business broadband as it is not designed for the size of the network it is running, and is consequently giving us all kinds of connectivity problems.

We have:

1 ADSL line
1 24 port Layer 2 switch
5 PCs in the administration area.
3 PCs in the students’ room
10 PCs in the computer room
5–10 wireless devices (varies)
2 additional wireless access points to provide complete coverage throughout the building
There are plans to purchase an additional 10 computers for the computer room in Q3 2011.

Obviously, we need something that is rock-solid stable. Price is an issue – we don’t want to spend more than is necessary, but at the same time we recognise that we have to spend some money on it.

Can you recommend a modem/router that includes a wireless access point?