There are lots of other posts about this in the forum, so just click around. Here's a good one: http://caloriecount.about.com/forums/weight-g ain/hosptial-gaining-sample-menu
Here is a 3,000 calorie meal plan (could easily become 3,500 if you added more to it) that works around healthy eating & ice-cream Some of the food on this list was food that I was using to gain weight when I first started my weight gain, but if you don't like some of the food, just switch it up to suit you! :)
Breakfast: Bowl of high fibre cereal with milk, 2 slices of toast with peanut butter & jelly/chocolate spread/almond butter, a piece of fruit & a smoothie/energy shake (try for no less then 700 calories)
Snack: Handful of mixed nuts & a cereal/chocolate bar (no less then 350 calories)
Lunch: Large jacket potato with cheese & beans or mayonnaise and tuna... (whatever you like) & some mixed vegetables with olive oil/ranch dressing OR poached eggs on toast & fresh vegetables, olive oil and cheese/mixed nuts (no less then 650 calories)
Snack: Some dried fruits & honey/syrup with yogurt (no less then 300 calories)
Dinner: Spaghetti & meatballs with cheese, stir fry with chicken, tofu, olive oil, fish... Whatever you like! :) (no less than 650 calories)
Dessert: Ice cream (as much as you like!) (no less then 350 calories)
This is the type of meal plan I had when I first started gaining, but now I mix it up every day :) If you struggle with breakfast (I can eat a lot at breakfast...), just make up for it throughout the rest of the day by eating more during snacks or extra helping with dinner. If this isn't the type of food you like, add in your favourites. The amount of calories is the most important thing. Get at least between 3,000/3,500 if your looking to gain weight at a relatively quick rate. Eat & enjoy the weight gain. You'll feel much better for it!
Hey, hope I can help out a bit :) If you want to increase your calories to 4,000 it can be pretty easy if you have fun with it! An example of a 4,000 calorie meal plan could be...
Breakfast: Pancakes/waffles with chocolate spread/maple syrup/yogurt and fruit with a milkshake/smoothie or a large bowl of cereal with full fat milk, topped with fruits & nuts and a couple of slices of toast with butter & jam, chocolate spread, etc... :) - no less then 750 calories
Snack: couple of handfuls of nuts with dried fruit & a chocolate bar - no less then 400 calories
Lunch: Really filled sandwich (filled with your favourite add ins) with a packet of crisps, a cereal bar and a piece of fruit with ensure - no less then 750 calories
Snack: carrots with hummus or avocado dip and a yogurt - no less then 400 calories
Dinner: Whatever you like (burger & chips, cheesy jacket potato, mixed vegetable stir fry with olive oil and chicken/tofu or even a take-out! - no less than 750 calories
Dessert: 4 scoops of ice cream with any toppings you like (cherries, chocolate, sprinkles, cookie dough <3 (a personal favourite!) - no less then 500 calories
Supper: A small bowl of cereal/soup or some blueberries with almonds... - no less then 300 calories
The bare minimum you should be getting with this type of meal plan is 3,850 calories. Make sure you pick calorie dense foods & you can't go wrong. Eat a rainbow & enjoy!
It can be really hard to gain weight--especially if you're active. I needed almost 5000 calories at one point. Generally the best thing is low-volume, high calorie foods. Try to drink a lot of things with calories (like juice, smoothies, full-fat milk, gatorade). Nuts/trail mix and peanut butter are also good. Dried fruits (raisins, etc). And of course things like chocolate and ice cream are always fun! Also, carnation instant breakfast is an easy thing to add to milk (130 calorie packet you mix with milk=250+ calorie drink).
also try to have 3 meals and 3 snacks a day if you can.
Here's a sample meal plan:
Breakfast: large bagel (300 cals) with 2 TB peanut butter (190); 12 oz whole milk (225) with 1 carnation instant breakfast (130); 1 banana (90) ~~950 calories
Snack: yogurt (150) and 1/4 cup nuts (175) = 325
Lunch: turkey sandwich (3-4oz turkey) , juice (120), chips (170) small salad with dressing (100) = 750 calories
Snack: smoothie (1 cup whole milk, yogurt, 2TB peanut butter, fruit) 
Dinner: pasta, pesto, chicken, salad with dressing, juice [~850]
Snack: Ice cream, nuts, fruit, etc
The side effects of allergy medications keep some people from using them. Natural remedies can be a great alternative, but some are more effective than others.