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