Ionisers and air purifiers are great - the first makes the pollen 'drop' out of the atmosphere and to floor level while the second clears the pollen out of the air. With both you need to make sure you give your house a dusting regularly to pick up the pollen that collects as it drops - microfibre cloths are fab for this.
Also, I know it's horrible when the weather is lovely, but it's really worth shutting your windows before sunset so that all the pollen dropping down in the atmosphere doesn't waft into your home and give you a sleepless night. I pull my blinds down in the evening to keep my flat cool instead. Blocks out the lovely sun but keeps my flat pollen-free.
Finally, when my hayfever (and other allergies - to dust, cat hair etc - what fun!) is bad I fill up the sink with cool water and 'dunk' my face in it and give the inside of my nose a quick wash to get rid of the pollen. I also shower in the evening and wash my hair to get rid of any pollen that I've picked up during the day.
It might all seem like a hassle but it's helped me more than any antihistamines.