1. Network Congestion - how many internet-enabled devices do you have connecting regularly?
2. Bandwidth Contention - do you live in a densely populated area? Verizon don't/won't be sending out bandwidth specifically to you, they just limit what can go down your ADSL line. If alot of people in the area use Verizon's DSL you'll always be contending with them for bandwidth
3. What is the wireless standard that your router supports? e.g. 802.11g. If your router is giving out B or N band signal, and your devices only support G band, there's part of the problem.
4. WPA/2 - If your wireless isn't encrypted/secured, then people could be connecting and congesting up your LAN, like Chipeater said.
5. Do you get the same problem when you surf using a hardwired/cabled connection? Plug a cat5 cable into your router and then into a laptop or PC, see if the sporadic d/cs etc. keep happening. If they don't, then the router is fully functional, it's only a wireless problem.
6. Check the cables running into your router from the wall/ISP; a loose BNC connector could cause problems.
7. Type your router's private IP (e.g. 192.168.x.y) into a web browser and enter your admin username and password, give the router a reset. Only do this is you don't have any port forwarding/advanced settings, or they will get erased and you'll have to do it all again.
thats all i can think of right now.