For cheap plants of good quality i use greenline

For High quality plants I would go for tropica plants - probably from Richard at aqua essentials. If I was feeling brave - apparently Pets @ Home stores stock tropica plants. I would only check them out on delivery day - they aren't kept in the best of condition.

For general fish equipment I tend to use Aquatics Online who have great prices and deliver promptly.

For Unusual mosses and cheap CO2 glassware I use Mike at Aquatic Magic an ebay store based in Malaysia.

For delivery of unusual fish types that I cant seem to track down in other places, I always try Monty at Tri Mar aquaria